The 1925 Geneva Convention and Cannabis

The meeting that quietly changed cannabis history

Where did international cannabis control actually begin? Most people point to the United States' Marihuana Tax Act of 1937, or to the 1961 Single Convention on Narcotic Drugs. Both matter. But the 1925 Geneva Convention, agreed at the Second International Opium Conference held in Geneva, was the first time cannabis was formally folded into an international drug control treaty, almost four decades before the Single Convention.

That conference is mostly remembered as an opium negotiation. The cannabis amendment was almost an afterthought. Almost.

The story tends to get distorted in both directions. Some accounts ignore it entirely, jumping straight from the early twentieth century to the 1960s. Others treat Geneva as the decisive moment that sealed cannabis's fate worldwide. Neither framing is quite right, and I think the more accurate version is more interesting than either. The meeting was a product of its time: a diplomatic setting in which a handful of delegates, working under the auspices of the League of Nations, were trying to tidy up a patchwork of national drug rules. If you want the wider story of how those rules took shape, the piece on the origins of cannabis prohibition sets out the broader context, and this article stays focused on one conference and what it did.

What the 1925 Geneva Convention actually said

The 1925 International Opium Convention, formally the Agreement Concerning the Manufacture of, Internal Trade in and Use of Prepared Opium, was primarily concerned with opiates and cocaine. When cannabis entered the negotiations, it did so late, and through an unexpected door.

The Egyptian delegate, Dr El Guindy, gave a speech arguing that hashish (the resin form of Cannabis sativa) was a serious social problem in Egypt and other parts of the Near East, and that it deserved the same international controls as morphine and cocaine. His argument found support from a South African delegation with similar concerns about dagga, the locally common term for cannabis. Readers curious about how that history echoes in present-day rules can look at cannabis law and access in South Africa.

The final treaty included a provision restricting the export of Indian hemp, specifically the resin, the preparations of it, and the plant parts "from which the resin has not been extracted", to countries that had issued official certificates of legitimate use. In practical terms, this placed cannabis alongside the controlled opium and cocaine alkaloids for the first time in international law.

A quick note on terminology, because it trips people up. An export control is a rule about what can cross a border and under what paperwork. It is not the same as a ban on possession, supply or use inside a country. The certificate system meant that an importing government had to vouch for a legitimate purpose, which left a great deal of day-to-day policy in national hands.

So it did not ban cannabis globally. The language was about export controls and official certificates, not criminalisation per se. But it did establish the foundational logic that cannabis was a dangerous substance requiring international oversight, a logic that the 1961 Single Convention would later take much further.

The science (or lack of it) behind the 1925 decision

Here is where a researcher's instincts kick in: what was the evidentiary basis for the Egyptian and South African delegates' claims?

Thin, to put it charitably. There were anecdotal reports of mental illness and social disorder linked to hashish use in Egypt, but no controlled studies, no pharmacological data, and no systematic epidemiological evidence. The Cannabis sativa plant's active compounds, what we now know as cannabinoids, including tetrahydrocannabinol (THC), the primary psychoactive constituent, weren't even isolated until 1964, when Raphael Mechoulam and Yechiel Gaoni published their structural characterisation of THC. In 1925, nobody knew what was actually in the plant. They were, in effect, scheduling a chemistry they didn't yet understand.

That gap is easier to grasp against the wider history of plant chemistry. Opium and coca had already given up their principal alkaloids to chemists, which is part of why they were easier to regulate with some precision; the background is covered in isolation of the first plant alkaloids. Cannabis was a different proposition, a plant with a complex mixture of constituents that nobody had yet characterised.

The endocannabinoid system, the network of receptors, endogenous ligands and enzymes that cannabis compounds interact with, wouldn't be described until the late 1980s and early 1990s. The concept that the body produces its own cannabis-like molecules, such as anandamide, was entirely unknown to every delegate in that Geneva conference room. They were making policy decisions about a biological system they had no idea existed.

I find that genuinely striking. Not in a "therefore prohibition was obviously wrong" way; that's a separate argument, and I'd rather not make it here. But if you're evaluating how that 1925 decision came to be made, "no scientific basis whatsoever" is a fair description.

Who pushed back, and why it didn't work

Several delegates opposed including cannabis in the 1925 treaty. India, then under British administration, was a significant voice. Indian hemp had deep cultural, religious, and economic roots across the subcontinent, and the British Indian delegation argued that its use in traditional contexts was quite different from the hashish problem described by the Egyptian delegation. The Indian Hemp Drugs Commission of 1894, one of the more methodologically serious drug investigations of that era, had concluded that moderate cannabis use was largely harmless and should not be prohibited.

That perspective was outvoted.

It is worth pausing on why. International conferences of this kind run on negotiation, not on weighing the best available data. A delegation with a vivid, locally urgent story about social harm can carry a room more easily than one arguing that a long-standing traditional practice is being misdescribed. The Indian delegation was, in effect, defending a nuanced position against a simpler narrative, and nuance rarely wins a vote.

There's a reasonable argument, and historians like David Bewley-Taylor have developed it, that the British and American delegations had complicated, sometimes contradictory positions across these interwar drug conferences, and that the inclusion of cannabis owed as much to political manoeuvring as it did to genuine public health concern. I reckon that's broadly correct, though it pays to be careful about retroactively simplifying what were genuinely messy diplomatic negotiations.

The road from 1925 to the Poisons Standard

The 1925 Convention's export-control framework set a precedent. The 1936 Geneva Convention for the Suppression of the Illicit Traffic in Dangerous Drugs tightened things further. Then came the 1961 Single Convention on Narcotic Drugs, the document that placed cannabis in Schedule IV (its most restrictive category) alongside heroin, a classification widely criticised by researchers ever since. For the legal meaning of that sort of listing, the glossary entry on a controlled substance is a useful companion.

Australia's own scheduling framework, now codified in the Therapeutic Goods Administration's Poisons Standard, traces part of its cannabis scheduling lineage to these international treaty obligations. THC and cannabis preparations sat in Schedule 9 (prohibited substances) in Australia for decades. The partial rescheduling that moved certain cannabidiol preparations to Schedule 4 (prescription only) from 2021, and the introduction of the Authorised Prescriber pathway and Special Access Scheme for medicinal cannabis, represent significant departures from that inherited framework, though Schedule 9 status still applies broadly to cannabis outside approved regulatory pathways. The federal regulator that oversees the import and supply side of this is described in the Office of Drug Control article.

For context: cannabidiol (CBD) at certain doses moved to Schedule 4 under the Poisons Standard amendment in 2020 (effective February 2021), making low-dose CBD products available by prescription. This was a domestic regulatory decision, not required by international treaty, and it illustrates how much latitude national regulators actually have to diverge from the 1925 framework when political conditions allow.

What the history does and doesn't tell us

One thing the 1925 record makes clear: the international drug control system was built on a series of political negotiations, not a coherent body of pharmacological evidence. That's not a conspiracy claim; it's just what the historical documents show. The chemistry of compounds like CBD was unknown, the receptor targets now described as CB1 and CB2 receptors were undiscovered, and the concept of plant-derived medicine operating through specific endogenous systems was decades away.

What it doesn't tell us, and this is where I see a lot of popular history go wrong, is that the absence of evidence in 1925 settles any question about whether cannabis compounds have risks or effects. Those are empirical questions, and the contemporary research record on cannabinoids is large, genuinely complicated, and full of caveats. Knowing that the original scheduling decision was poorly evidenced doesn't automatically validate any particular claim about what cannabis does or doesn't do. The two things are logically separate.

The pattern is a familiar one in any era. Early twentieth-century colonial medical reports on cannabis, for instance, often made confident claims on the basis of little or no controlled methodology. That's a good reminder that "expert consensus at the time" and "rigorous evidence" aren't the same thing, including in our own period.

The 1925 Geneva Convention is a starting point for understanding why cannabis carries the regulatory weight it does today. It's not an explanation for what cannabis actually is, pharmacologically. Those are different histories, and the second one is still being written. For the medical side of that second history, a history of cannabis in medicine picks up where the treaty story leaves off.

How to read historical drug-policy claims critically

The Geneva story offers a handy template for reading any historical account of drug policy. A few habits help, and none of them require specialist training.

First, separate the treaty text from the commentary about it. What a convention literally says, here, export controls and certificates, is often narrower than what later writers claim it did. Going back to the primary wording, or to a reputable summary such as the UNODC and WHO material listed below, is the quickest way to catch an overstatement.

Second, ask what kind of evidence a claim rests on. An anecdote, a government commission report and a controlled study are different things, and a policy decision can lean on any of them. The Indian Hemp Drugs Commission of 1894 was a structured inquiry, whereas the reports presented to the 1925 delegates were largely anecdotal. If you want a practical guide to weighing stronger forms of evidence, reading a systematic review explains what to look for.

Third, watch for the leap from "this decision was poorly evidenced" to "therefore the opposite claim is proven". Weak grounds for a rule do not, on their own, establish anything about a substance. And finally, check the date. Terms, classifications and legal status shift over time, so anything about current Australian scheduling should be confirmed against the Therapeutic Goods Administration's own published material rather than a secondary summary, including this one. For wider background on the League of Nations itself, the League of Nations Wikipedia entry is a reasonable starting point.

Sources

• A History of Cannabis Control, United Nations Office on Drugs and Crime (UNODC) Bulletin
• Scheduling Handbook: Guidance on the Poisons Standard, Therapeutic Goods Administration (TGA)
• Cannabis policy reform in the context of the international drug control system; NCBI/PubMed Central
• WHO Expert Committee on Drug Dependence: Cannabis and cannabis-related substances, World Health Organization

Hannah Bui, Evidence & research-literacy writer