From Calcutta to Geneva: medicine, inquiry and the making of prohibition

In the space of roughly a century, cannabis travelled an extraordinary road in the Western imagination. In the late 1830s a professor in Calcutta began giving hemp preparations to patients with tetanus, cholera and rheumatism, and within a few years "Cannabis indica" had found a place in British and American medical practice. By the 1940s it had been struck out of the United States Pharmacopeia, made the object of a federal tax designed to stop its use, and placed under international treaty controls that would soon harden into some of the strictest ever applied to a plant. Along the way, a remarkably thorough colonial inquiry concluded that moderate use did little harm, and was largely ignored. So, in the decades that followed, were several more.

This article follows that road, drawing in particular on the historian James Mills's study of the British Empire and cannabis (Mills, 2003). The story is neither one of a medicine unjustly banned nor of a dangerous drug sensibly brought under control. It is about how medical fashion, imperial administration, moral campaigning and diplomatic bargaining interacted, and about how evidence repeatedly failed to steer policy. Earlier articles in this series cover the plant's origins, prehistory, ancient ritual use and medieval trade; the final one takes up the science and reforms of recent decades. As throughout, this is history, not advice on growing, using or prescribing cannabis.

The setting: colonial medicine and the search for new drugs

Materia medica in an age of empire

"Materia medica", a term inherited from the Latin title of Dioscorides' first-century herbal, meant the body of knowledge about substances used as medicines: where they came from, how they were prepared and what they were thought to do. Before synthetic chemistry, most of those substances were plants or plant products. Opium, cinchona bark (the source of quinine), digitalis from the foxglove and many others formed the core of the physician's armoury.

Empire and medicine were closely entangled. European powers ruled or traded across regions with rich medical traditions and unfamiliar floras, and colonial doctors and chemists had both the opportunity and the incentive to investigate local remedies, whether from scientific curiosity or because a cheap, locally available drug was of value to administrations and armies. India, with its long Ayurvedic and Unani traditions and wide everyday use of hemp drugs, was an obvious place to look. At the same time, experimental method was gaining ground: chemists had begun isolating active principles such as morphine from opium, and physicians increasingly tested remedies on animals and then patients and reported the results in a growing world of medical journals.

Hemp drugs in India

Hemp drugs were already woven into Indian social and religious life. Three main preparations were distinguished: bhang, made from the leaves and used especially in drinks; ganja, the dried flowering tops; and charas, the resin. They were associated particularly with Shaivite devotion and with festivals. For the colonial state they were also a taxable commodity: the government of India drew excise revenue from hemp drugs, a fact that coloured its later response to calls for prohibition (Mills, 2003).

William O'Shaughnessy in Calcutta

The professor and his experiments

The modern Western medical career of cannabis began with William Brooke O'Shaughnessy, Professor of Chemistry and Materia Medica at the Medical College of Calcutta, one of the institutions through which Western medical teaching was established in British India. O'Shaughnessy, an Irish-born physician in the service of the East India Company, was an energetic figure; he is remembered in India at least as much for his later work establishing the electric telegraph as for his pharmacology.

He published experimental and clinical observations on Indian hemp in the Transactions of the Calcutta medical society in 1838–1839, then revised them for a British readership in the London Provincial Medical Journal in 1843 (O'Shaughnessy, 1843). The 1843 title signals his interests: the preparations of "Indian hemp, or gunjah", their effects "on the animal system in health", and "their utility in the treatment of tetanus and other convulsive diseases".

His method was typical of the experimental medicine of the time. He began with experiments in animals before reporting trials of hemp preparations in rheumatism, cholera, tetanus and infantile convulsions (O'Shaughnessy, 1843). These were not trivial complaints. Cholera was a terrifying epidemic killer; tetanus, before antitoxins and intensive care, typically killed through exhausting muscular spasm; convulsions in infants were frightening and dangerous. Physicians had few effective treatments for any of them, which helps explain why a possible new remedy could be greeted with enthusiasm.

Measured claims, and a careful disclaimer

Read today, O'Shaughnessy's writing is striking for its balance. He did not present cannabis as harmless. Instead he compared it with the intoxicants most familiar to his readers, judging the "evil sequels" attributed to the drug less "numerous" or "formidable" than those of alcohol or opium (O'Shaughnessy, 1843). That is a comparative judgement, not a claim of harmlessness, and it anticipates a recurring theme: the question was rarely whether cannabis could do harm, but how its harms compared with those of substances society already tolerated.

Shortly after the paper appeared, he wrote to the journal to "disclaim any wish to advance these preparations as specifics in the treatment of tetanus" (O'Shaughnessy, 1843). A "specific", in the medical language of the day, was a remedy believed to act directly and reliably against a particular disease, as quinine was thought to act against malaria. In disowning that claim, O'Shaughnessy stepped back from the most dramatic reading of his own results. The founder of Western cannabis therapeutics was himself wary of overclaiming, a caution that later advocates and opponents have not always shared.

From Calcutta to London and beyond

O'Shaughnessy's work introduced "Cannabis indica" into British and then American practice (Zuardi, 2006; Mills, 2003). In pharmacy the name came to denote drug preparations derived from Indian plants, as opposed to European hemp grown for fibre: a commercial and medical label as much as a botanical one. Knowledge travelled from Indian practitioners and markets, through a colonial medical college, into the journals of the metropolis. Cannabis entered Western medicine as a product of empire, and, as Mills (2003) shows, empire would also shape its exit.

Moreau de Tours and the Parisian experiment

Hashish as a model of madness

While O'Shaughnessy tested hemp as therapy, a French psychiatrist approached it from a different direction. Jacques-Joseph Moreau, known as Moreau de Tours, had encountered hashish on travels in the Middle East and North Africa, and he was interested less in what it might cure than in what it might reveal about the mind.

In Du hachisch et de l'aliénation mentale (1845), Moreau used hashish intoxication, including his own, as an experimental model of insanity (Moreau, 1845). His reasoning was that the altered states produced by the drug resembled some symptoms of mental illness, so that by inducing them deliberately and observing them closely, from the inside, a physician might understand madness better. The book is an early example of a psychoactive drug used as a tool for psychiatric research, an approach that would recur in very different forms in the twentieth century. Using one's own experience as data raises obvious questions of objectivity, but it reflects the ambitions of a young discipline trying to establish itself as a science of the mind long before brain imaging or modern pharmacology.

The Club des Hashischins

Moreau's circle overlapped with the Parisian literary Club des Hashischins, a group of writers and artists who gathered in the 1840s to take hashish and record their experiences. Writers such as Théophile Gautier and Charles Baudelaire are associated with it, and their accounts helped fix in the European imagination an image of hashish as exotic, visionary and somewhat dangerous, an image indebted to the same Orientalist fantasy that produced the legend of the hashish-crazed "Assassins", discussed in the article on the medieval world.

The contrast is instructive. In Calcutta, cannabis was a remedy to be tested on bodies; in Paris, it was a window on the mind and a literary sensation. The tension between medicine and intoxication runs through everything that followed.

Pharmacopoeias, prescriptions and slow decline

What a pharmacopoeia is

In the second half of the nineteenth century, cannabis extracts and tinctures were entered in Western pharmacopoeias and prescribed for pain, spasm, insomnia and other conditions (Zuardi, 2006). A pharmacopoeia is an official book of drug standards. It lists the medicines recognised by a country's medical establishment and sets out how each should be identified, prepared and tested for purity. Its purpose is consistency: a tincture made by one pharmacist should match one made by another, so that a prescription means the same thing wherever it is filled. The United States Pharmacopeia first appeared in 1820 and a unified British Pharmacopoeia in 1864. Inclusion signalled that a substance had become part of mainstream, regulated medicine, and for several decades cannabis preparations were simply one drug among many, alongside opium, chloral and the other sedatives and analgesics of the day.

Why crude plant drugs were a problem

Their use declined from the late nineteenth century. Contributing factors included the variable potency of crude preparations, the instability of extracts, the rise of synthetic analgesics and hypnotics, and finally legal restriction (Zuardi, 2006; National Academies of Sciences, Engineering, and Medicine, 2017).

The first two are characteristic problems of plant medicine before modern analytical chemistry. A tincture was only as consistent as the plant material that went into it, and that material varied enormously with where it was grown, when it was harvested, and how it was dried, stored and shipped. Nobody in the nineteenth century knew what the active substance was: the principal psychoactive compound was not isolated and its structure established until 1964, a story told in the final article of this series. Without knowing what to measure, manufacturers could not standardise their products. Extracts also deteriorated on the shelf, so a preparation might lose strength over time. A drug too weak to work one week and unexpectedly strong the next was hard to use safely or effectively.

Opium offered a telling contrast. Its main active principle, morphine, could be purified and given in exact amounts, especially once the hypodermic syringe came into use in the mid-nineteenth century. Cannabis had no such advantage.

The rise of synthetic drugs

The third factor was competition. The late nineteenth and early twentieth centuries saw the birth of the modern pharmaceutical industry, much of it built on synthetic organic chemistry. Chloral hydrate came into use as a sedative from 1869, aspirin was marketed from 1899, and the barbiturates, from the first years of the twentieth century, became the dominant sleeping drugs for decades. Each offered what cannabis could not: a pure compound, reliably dosed.

In this light, the medical decline of cannabis looks less like a conspiracy than the ordinary fate of many crude botanical drugs in the age of synthetic chemistry. What made cannabis different was the fourth factor, legal restriction, which arrived as its medical use was already waning and ensured that it could not easily be revived.

Removal from the US Pharmacopeia, 1942

Cannabis was removed from the US Pharmacopeia in 1942, in its twelfth edition, USP XII (National Academies of Sciences, Engineering, and Medicine, 2017; Zuardi, 2006). By then the Marihuana Tax Act of 1937, discussed below, had made medical use administratively burdensome, and the drug had long since lost ground to synthetic competitors. The removal confirmed, rather than caused, its departure from mainstream American medicine, almost exactly a century after O'Shaughnessy's work.

The Indian Hemp Drugs Commission, 1893–94

Temperance, missionaries and the asylum question

While cannabis was fading from Western prescriptions, its use in India became the subject of heated political argument in Britain. The temperance movement, which began as a campaign against the abuse of alcohol, had grown by the later nineteenth century into one of the largest and best-organised moral reform movements in British public life, with its own societies, newspapers, petitions and allies in Parliament. Closely linked were missionary societies and campaigners against the opium trade, who saw the Empire's profits from intoxicants as a moral stain. These groups were adept at turning concern about the conduct of empire into political pressure at Westminster.

Their attention fell on hemp drugs partly because of Indian asylums. Campaigners linked ganja to insanity in Indian asylums, pointing to asylum returns that attributed some inmates' illness to the drug (Indian Hemp Drugs Commission, 1894; Mills, 2003). If the colonial government profited from a drug that drove its subjects mad, the moral case seemed clear. Under this pressure, the Government of India appointed the Indian Hemp Drugs Commission in 1893.

Composition and method

The Commission had a president and six members, three of them Indian non-officials (Indian Hemp Drugs Commission, 1894). That composition mattered. A body made up entirely of British officials might have been dismissed as colonial self-justification; Indian members from outside government gave its findings broader standing and brought first-hand knowledge of the customs in question.

Its scale was remarkable. Between August 1893 and August 1894 it took evidence from 1,193 witnesses across India, and it published a report of some seven volumes and 3,281 pages (Indian Hemp Drugs Commission, 1894). It examined cultivation, preparation and trade, the extent and manner of consumption, effects on body, mind and morals, and arrangements for control. It recorded customs in rich detail: in Bengal, for instance, an infusion of the leaves was "commonly offered to every guest and member of the family on the last day of the Durga Puja" without being considered reprehensible (Indian Hemp Drugs Commission, 1894). By the standards of its time, and of many later inquiries, this was an empirically serious undertaking.

What the Commission concluded

Its central conclusions were clear: "the moderate use of hemp drugs is practically attended by no evil results at all", it "produces no injurious effects on the mind" and it "produces no moral injury whatever". It did not dismiss the risks, accepting that "excessive use" could be "very injurious" (Indian Hemp Drugs Commission, 1894). The distinction between moderate and excessive use was the heart of its analysis, as it would be for later inquiries in Britain, the United States and Canada.

On the question that had prompted much of the agitation, Mills (2003) shows that the Commission found the asylum statistics linking cannabis to insanity to be inflated. Having weighed the evidence, it recommended regulation and taxation, not prohibition (Indian Hemp Drugs Commission, 1894). Suppressing a practice so widespread, and so bound up with religion and hospitality, would in its view have been neither justified nor practicable.

Reading the Commission in its colonial context

It is tempting to hold the Commission up as a model of evidence-based policymaking, and in some respects it deserves that reputation. But modern readers should note both its empirical seriousness and its colonial fiscal context (Mills, 2003). Excise is a tax on the production or sale of goods within a country, and in British India the hemp drug trade was managed through licences and duties. Prohibition would have meant giving up that revenue and enforcing a ban against widespread, socially accepted practices. Regulation and taxation suited the administration very well.

None of this means the Commission's findings were wrong. It means that its conclusions also served the interests of the state that commissioned them, and that the historian must hold both facts in view. Assessments of cannabis have rarely been made in a political vacuum, whether the pressure came from moral campaigners, revenue officials or diplomats.

Geneva, 1925: cannabis enters international law

Before cannabis: Shanghai and The Hague

International drug control began with opium. A commission met in Shanghai in 1909, followed by the International Opium Convention signed at The Hague in 1912, the first international drug control treaty. It addressed opium, morphine and cocaine. It did not control cannabis (Mills, 2003).

An international convention is a treaty, binding on the states that ratify it. Drug conventions typically oblige their parties to limit the production, trade and use of listed substances, to require authorisations for import and export, to report to an international body, and to pass domestic laws giving effect to these obligations. The conventions do not themselves create criminal offences; each state must legislate. This is why international agreements in this story are always followed by national statutes and regulations. After the First World War, responsibility for drug control passed to the League of Nations.

The Second Opium Conference and the Egyptian case

Cannabis entered international law at the Second Opium Conference in Geneva in 1924–25, largely at Egypt's initiative. The Egyptian delegate made what a reviewer of Mills summarises as a "powerful, and successful, case against hemp drugs". That case relied heavily on a report by a British doctor who had run the Egyptian Lunacy Department while Egypt was a British protectorate (Mills, 2003).

The irony is considerable. Three decades after a British commission in India had found moderate use largely harmless and asylum statistics inflated, evidence from a British doctor running asylums elsewhere in the empire was used to argue for international control. Different branches of the imperial system had reached different conclusions about the same drug, and it was the more alarming one that entered international law. In Mills's phrase, "The many tentacles of the empire seem to have become entangled on the issue of cannabis" (Mills, 2003).

Such conferences were not neutral scientific forums. Delegations represented national interests, traded concessions and sought allies for their own priorities, and the larger negotiations concerned opium and coca. Cannabis was a relatively minor item on a crowded agenda, and its inclusion owed as much to the dynamics of the conference as to any comprehensive review of evidence.

What the 1925 Convention did

The resulting 1925 International Opium Convention brought "Indian hemp" under international controls on import and export (Mills, 2003). International trade in the drug became subject to a system of authorisations, allowing governments to monitor and restrict cross-border movements. The convention did not itself prohibit domestic use everywhere, but it established cannabis as a drug of international concern within a framework that later treaties would greatly tighten.

The British response: 1928

In Britain, the convention led to domestic regulation. From 1928, possession of cannabis without medical authorisation became an offence under regulations made under the Dangerous Drugs Acts (Mills, 2003), the legislation through which Britain had implemented its earlier commitments on opium, morphine and cocaine.

Strikingly, little domestic debate preceded this step. Cannabis was not a widely discussed social problem in 1920s Britain; its control arrived because Britain had signed an international agreement. Mills's broader argument is that British prohibition "grew out of the politics of empire rather than scientific or rational assessment of the drug's use and effects" (Mills, 2003). The trajectory from colonial excise to criminal offence is the core of that argument.

The United States: the Marihuana Tax Act of 1937

A tax that was really a ban

The American route was different in form but similar in outcome. The Marihuana Tax Act of 1937 (Pub. L. 75-238, 50 Stat. 551), approved on 2 August 1937 and effective on 1 October 1937, effectively prohibited non-medical cannabis through a prohibitive transfer tax and registration scheme (Marihuana Tax Act, 1937).

Why a tax rather than a ban? At the time, the federal government's power to regulate health and personal conduct within the states was understood to be limited, but Congress's taxing power was broad. The Harrison Narcotics Act of 1914 had already used taxation to control opiates and cocaine, and the 1937 Act followed the same path.

A transfer tax is levied when goods change hands. Under the 1937 scheme, those who dealt in cannabis legitimately, such as importers, manufacturers, pharmacists and physicians, had to register and pay an occupational tax, and transfers had to be documented on official forms. Transfers to unregistered people were taxed at a punitive rate. Registration, paperwork and heavy tax together made non-medical trade practically impossible to conduct lawfully, while leaving a narrow, cumbersome channel for medical and industrial uses. A revenue measure functioned as a prohibition.

Anslinger and the Federal Bureau of Narcotics

The Act's leading advocate was Harry J. Anslinger, the first Commissioner of the Federal Bureau of Narcotics, who testified at the congressional hearings. The Bureau had been created in 1930, and Anslinger led it for more than three decades, becoming one of the most influential figures in drug policy in the United States and internationally. The hearings were brief, and the American Medical Association raised objections, partly that the bill would burden doctors and pharmacists. Those objections did not prevent its passage.

A racialised campaign

Historians have documented how the campaign drew on racialised imagery of Mexican migrants and Black musicians. Newspaper stories and official rhetoric linked the drug to crime, violence and immorality, and attached those fears to groups already subject to prejudice. Not every supporter of the Act need have been motivated by racial animus, but racial anxieties supplied much of the campaign's emotional force.

What's in a spelling

Even the Act's title carries this history. The English spelling "marihuana" drew on Mexican Spanish usage, which Duvall (2019) traces back to African-derived terms. American physicians and pharmacists had generally spoken of "cannabis" or "Indian hemp". The new word helped frame the drug as foreign and novel, distinct from the familiar medicine in the pharmacy, at the very moment that medicine was being legislated out of practical use.

The Act remained in force until the US Supreme Court held parts of it unconstitutional in Leary v. United States (1969), and it was replaced by the Controlled Substances Act of 1970. By then, American prohibition had long since been projected onto the international stage.

The United Nations conventions

Consolidation: the Single Convention, 1961

After the Second World War the United Nations inherited the League's role and a patchwork of pre-war treaties. These were consolidated into the Single Convention on Narcotic Drugs, 1961, which opened for signature in New York on 30 March 1961 and entered into force on 13 December 1964 (United Nations, 1961). "Single" reflected its purpose: one comprehensive instrument in place of many. Under it, the UN Commission on Narcotic Drugs, a body of member states, decides changes to the lists of controlled substances, and the International Narcotics Control Board monitors compliance, with the World Health Organization advising on scheduling.

How the schedules work

A drug convention's key mechanism is its schedules. A schedule is simply a list, and each list carries a defined set of obligations: the more restrictive the schedule, the tighter the controls on production, trade, possession and use. Placing a drug in a schedule is a legal judgement about how it should be treated, and moving it changes the obligations of every party.

Cannabis and cannabis resin were placed in Schedule I and also in Schedule IV, the most restrictive category, reserved for drugs considered particularly dangerous and of little therapeutic value (UNODC, 2020). Schedule IV is not a separate tier but a subset of Schedule I drugs singled out for extra restriction, and it permits states to prohibit even medical and scientific use if they see fit. For a plant listed in Western pharmacopoeias within living memory, it was a striking verdict. Its later removal from Schedule IV belongs to the final article in this series.

Reservations and Article 49

In international law, a reservation is a statement by which a state, on signing or ratifying a treaty, excludes or modifies the legal effect of certain provisions for itself. Reservations let states join a treaty while preserving domestic practices that would otherwise breach it.

Article 49 of the Single Convention allowed transitional reservations for traditional non-medical use, but only temporarily. It required that "the use of cannabis for other than medical and scientific purposes must be discontinued as soon as possible but in any case within twenty-five years" of entry into force (United Nations, 1961), a deadline that fell at the end of 1989. The provision mainly affected South Asian states with established customary use. The very practices the Indian Hemp Drugs Commission had documented, and judged largely harmless in moderation, were now on an international timetable for abolition. Few contrasts in this history show more clearly how far legal status could drift from the conclusions of official inquiry.

The 1971 Convention on Psychotropic Substances

The Single Convention dealt with plant-derived narcotics. In the 1960s a wave of synthetic and semi-synthetic drugs, including hallucinogens, amphetamines and sedatives, prompted a second treaty, the 1971 Convention on Psychotropic Substances, agreed in Vienna. For cannabis, it added control of tetrahydrocannabinol isomers and dronabinol (UNODC, 2020). Now that the plant's principal psychoactive compound could be identified and synthesised, a defined chemical could be regulated as well as a plant. The result was a dual structure, plant and resin under the 1961 treaty and the isolated compound under the 1971 treaty, that has complicated international discussion ever since.

The United Kingdom: the Misuse of Drugs Act 1971

In the United Kingdom, the Misuse of Drugs Act 1971 implemented the international framework domestically. Still the foundation of British drug law, it divides controlled drugs into Classes A, B and C with different maximum penalties, placed cannabis in Class B, and created the Advisory Council on the Misuse of Drugs. Separate regulations sort drugs into schedules according to permitted medical use, a distinction that would become central to later debates about medicinal cannabis.

Official inquiries and dissent

Prohibition never lacked critics

Prohibition never lacked official critics. Around 1970, as cannabis use spread among young people in Western countries and arrests rose, governments in Britain, the United States and Canada each commissioned serious inquiries. Each reached conclusions more lenient than the law of the day.

The Wootton Report, 1968

In the United Kingdom, the Advisory Committee on Drug Dependence reported on cannabis in 1968. Known as the Wootton Report after Baroness Wootton, who chaired the sub-committee responsible, it found that the dangers of cannabis had been overstated (Advisory Committee on Drug Dependence, 1968). It did not call the drug harmless, but it questioned whether the legal treatment of users was proportionate to the evidence. The government of the day received it coolly, and its direct influence on the law was limited.

The Shafer Commission, 1972

In the United States, the National Commission on Marihuana and Drug Abuse, chaired by Raymond Shafer, a former Governor of Pennsylvania, reported in 1972 as Marihuana: A Signal of Misunderstanding. It recommended decriminalising possession for personal use (National Commission on Marihuana and Drug Abuse, 1972). The recommendation was notable because the Commission had been appointed under an administration publicly committed to a hard line on drugs. President Richard Nixon rejected it.

The Le Dain Commission, 1972

In Canada, the Commission of Inquiry into the Non-Medical Use of Drugs, chaired by the legal scholar Gerald Le Dain, published its report on cannabis in 1972, and it too argued for reform (Commission of Inquiry into the Non-Medical Use of Drugs, 1972). Like its British and American counterparts, it did not present cannabis as risk-free; it argued that the harms of criminalising users had to be weighed against the harms of the drug.

A recurring pattern

Like the Indian Hemp Drugs Commission eighty years earlier, these reports were largely set aside by governments of the time. That recurring pattern is itself historically significant.

The source review does not offer a single explanation, and it would be unwise to impose one. But the wider story suggests some reasons. By the 1960s, national governments were bound by international conventions that left little room for unilateral liberalisation. Drug policy had become a symbolic issue, bound up with anxieties about youth, protest and social change, so appearing lenient carried political costs whatever the evidence. And the institutions created to enforce prohibition had their own interests in its continuation. Inquiries could inform debate, but they could not easily overcome these pressures.

In 1894, 1968 and 1972, carefully assembled evidence pointed towards distinctions between moderate and excessive use and towards responses proportionate to actual harm. Each time the law moved more slowly, or in the opposite direction: official inquiries repeatedly reached more nuanced conclusions than the laws that followed them. When partial reversal came from the 1990s onwards, it came largely on medical grounds, driven by cannabinoid science, rather than because governments finally accepted these earlier reports.

Timeline: from Calcutta to Vienna

What we know, and what we don't

Historians of cannabis must steer between two polarised literatures, one inclined to present the plant as a persecuted panacea, the other to treat prohibition as self-evidently justified. Separating firm evidence from interpretation is the best defence against both.

What the evidence supports well

• The medical adoption was real and documented. O'Shaughnessy's publications, the conditions in which he tried hemp, and his caution about tetanus are well attested (O'Shaughnessy, 1843).
• The decline had several causes. Variable potency, unstable extracts, synthetic competitors and legal restriction all played a part, and medical decline was under way before the major prohibitive laws (Zuardi, 2006).
• The 1894 Commission was thorough and its conclusions lenient. Its witnesses, its distinction between moderate and excessive use, its scepticism about asylum statistics and its recommendation of regulation and taxation are on record (Indian Hemp Drugs Commission, 1894; Mills, 2003).
• International control began in Geneva in 1925, not at The Hague, with Egyptian advocacy central to it (Mills, 2003).
• The treaty architecture is a matter of public record: Schedules I and IV in 1961, the Article 49 phase-out, and the 1971 controls on THC (United Nations, 1961; UNODC, 2020).
• Later inquiries in the UK, US and Canada recommended more lenient approaches and were largely not acted upon.

Where interpretation and uncertainty remain

• How much weight to give empire. Mills's argument is persuasive and well documented, but it concerns British history in particular. Other countries reached prohibition by other routes, and the relative weight of diplomacy, moral campaigning, racial anxiety and public health concern varied.
• The motives behind the 1894 conclusions. The Commission's seriousness and its fiscal context are both real; how far revenue interests shaped its findings is hard to establish.
• The Geneva negotiations. Egypt's role is clear in outline, but our picture of the Egyptian case comes partly through secondary summaries of archival work.
• The American campaign. That it drew on racialised imagery is well documented; how decisive that imagery was, compared with bureaucratic ambition and other factors, remains debated.
• Non-European perspectives. We know far more about what British, American and League officials thought than about how Indian, Egyptian and other colonised societies experienced the coming of control. Archival work on non-European regulatory histories is one of the most promising directions for research.

Looking back from Geneva

Between Calcutta and Geneva, and on to New York and Vienna, cannabis was transformed from a promising colonial medicine into an internationally controlled substance. The plant did not change; the institutions, interests and fears through which it was viewed did. A careful colonial professor, a curious French psychiatrist, a revenue-conscious colonial government, a determined Egyptian delegation, an ambitious American bureaucrat and a succession of treaty negotiators each played a part.

Running through it all is the quiet persistence of evidence gathered and then not used. The inquiries of 1893–94, 1968 and 1972 were produced in very different worlds, but they shared a willingness to distinguish moderate from excessive use and to weigh the harms of the law alongside the harms of the drug. That the law so consistently moved another way may be the most important lesson of this part of the history. The final article in the series takes up what happened when science and medicine began to push back.

Sources

Advisory Committee on Drug Dependence (1968) Cannabis (the Wootton Report). London: HMSO.

Commission of Inquiry into the Non-Medical Use of Drugs (1972) Cannabis (the Le Dain Commission report). Ottawa: Information Canada.

Duvall, C.S. (2019) The African Roots of Marijuana. Durham, NC: Duke University Press. doi:10.2307/j.ctv11hpqx7.

Indian Hemp Drugs Commission (1894) Report of the Indian Hemp Drugs Commission, 1893–94. Simla: Government Central Printing Office.

Marihuana Tax Act (1937) Pub. L. No. 75-238, 50 Stat. 551 (approved 2 August 1937).

Mills, J.H. (2003) Cannabis Britannica: Empire, Trade, and Prohibition 1800–1928. Oxford: Oxford University Press.

Moreau, J.-J. (de Tours) (1845) Du hachisch et de l'aliénation mentale: études psychologiques. Paris: Fortin, Masson et Cie.

National Academies of Sciences, Engineering, and Medicine (2017) The Health Effects of Cannabis and Cannabinoids: The Current State of Evidence and Recommendations for Research. Washington, DC: The National Academies Press. Available at: https://www.ncbi.nlm.nih.gov/books/NBK425762/.

National Commission on Marihuana and Drug Abuse (1972) Marihuana: A Signal of Misunderstanding. Washington, DC: US Government Printing Office.

O'Shaughnessy, W.B. (1843) 'On the preparations of the Indian hemp, or gunjah (Cannabis indica); their effects on the animal system in health, and their utility in the treatment of tetanus and other convulsive diseases', Provincial Medical Journal and Retrospect of the Medical Sciences, 5(122), pp. 343–347; 5(123), pp. 363–369. Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC2490264/.

United Nations (1961) Single Convention on Narcotic Drugs, 1961. New York, 30 March 1961; entered into force 13 December 1964. United Nations Treaty Series, vol. 520.

UNODC (2020) CND votes on recommendations for cannabis and cannabis-related substances. Vienna, 3 December 2020. Available at: https://www.unodc.org/unodc/en/frontpage/2020/December/cnd-votes-on-recommendations-for-cannabis-and-cannabis-related-substances.html.

Zuardi, A.W. (2006) 'History of cannabis as a medicine: a review', Revista Brasileira de Psiquiatria, 28(2), pp. 153–157. doi:10.1590/S1516-44462006000200015.