Did the 1925 Geneva Convention ban cannabis globally?

No. The 1925 Convention introduced export controls on Indian hemp and its resin, requiring official certificates for legitimate trade. It did not criminalise cannabis domestically in signatory nations — that kind of prohibition came later, most significantly through the 1961 Single Convention on Narcotic Drugs, which placed cannabis in its most restrictive scheduling category.

Why was cannabis included in the 1925 Convention if the science wasn't there?

The inclusion was driven primarily by political advocacy, notably from the Egyptian and South African delegations, who cited social concerns about hashish and dagga use respectively. There was no pharmacological research base — the active compounds in cannabis weren't isolated until 1964, and the endocannabinoid system wasn't described until the late 1980s. The decision was made without knowledge of the biology involved.

How does the 1925 Convention relate to Australia's current cannabis scheduling?

Australia's Poisons Standard scheduling of cannabis is partly rooted in international treaty obligations that trace back to the 1925 framework, consolidated by the 1961 Single Convention. Cannabis outside approved regulatory pathways remains Schedule 9 (prohibited) in Australia. However, domestic reforms — such as the rescheduling of low-dose cannabidiol to Schedule 4 in 2021 and the Authorised Prescriber and Special Access Scheme pathways for medicinal cannabis — demonstrate that national regulators have significant room to diverge from the inherited international framework.

Who opposed cannabis being included in the 1925 Convention?

The British Indian delegation was a notable opponent, arguing that traditional use of cannabis in India was culturally significant and distinct from the hashish problems described by other delegates. The 1894 Indian Hemp Drugs Commission had reached relatively permissive conclusions, and India's position reflected that. Despite this opposition, the export-control provisions were adopted.

Does the flawed historical basis of cannabis scheduling tell us anything about cannabis's actual pharmacology?

Not directly. The fact that the 1925 decision lacked a scientific foundation is a statement about the history of drug policy, not a pharmacological conclusion. Questions about the effects and risks of cannabinoids like THC and CBD are empirical matters answered by contemporary research, which is ongoing and complex. The two issues — how scheduling came to be, and what cannabinoids actually do biologically — are logically separate.

The 1925 Geneva Convention and Cannabis

By Hannah Bui · 8 May 2026 · 7 min read

Open book with botanical illustrations of roses.

The meeting that quietly changed cannabis history

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

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

I've been reading through the League of Nations records on this for a while now, partly because I think the story gets distorted in both directions , either ignored entirely, or treated as the decisive moment that sealed cannabis's fate worldwide. Neither framing is quite right.

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.

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.

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's where my 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.

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.

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's worth being 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.

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.

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.

Between sea swims last winter I went back through a stack of early 20th-century colonial medical reports on cannabis, and honestly, the number of confident claims made on the basis of zero controlled methodology is sobering. It's a good reminder that "expert consensus at the time" and "rigorous evidence" aren't the same thing in any era, including ours.

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.

Sources

, Hannah Bui, Evidence & research-literacy writer

Common questions

Did the 1925 Geneva Convention ban cannabis globally?: No. The 1925 Convention introduced export controls on Indian hemp and its resin, requiring official certificates for legitimate trade. It did not criminalise cannabis domestically in signatory nations — that kind of prohibition came later, most significantly through the 1961 Single Convention on Narcotic Drugs, which placed cannabis in its most restrictive scheduling category.
Why was cannabis included in the 1925 Convention if the science wasn't there?: The inclusion was driven primarily by political advocacy, notably from the Egyptian and South African delegations, who cited social concerns about hashish and dagga use respectively. There was no pharmacological research base — the active compounds in cannabis weren't isolated until 1964, and the endocannabinoid system wasn't described until the late 1980s. The decision was made without knowledge of the biology involved.
How does the 1925 Convention relate to Australia's current cannabis scheduling?: Australia's Poisons Standard scheduling of cannabis is partly rooted in international treaty obligations that trace back to the 1925 framework, consolidated by the 1961 Single Convention. Cannabis outside approved regulatory pathways remains Schedule 9 (prohibited) in Australia. However, domestic reforms — such as the rescheduling of low-dose cannabidiol to Schedule 4 in 2021 and the Authorised Prescriber and Special Access Scheme pathways for medicinal cannabis — demonstrate that national regulators have significant room to diverge from the inherited international framework.
Who opposed cannabis being included in the 1925 Convention?: The British Indian delegation was a notable opponent, arguing that traditional use of cannabis in India was culturally significant and distinct from the hashish problems described by other delegates. The 1894 Indian Hemp Drugs Commission had reached relatively permissive conclusions, and India's position reflected that. Despite this opposition, the export-control provisions were adopted.
Does the flawed historical basis of cannabis scheduling tell us anything about cannabis's actual pharmacology?: Not directly. The fact that the 1925 decision lacked a scientific foundation is a statement about the history of drug policy, not a pharmacological conclusion. Questions about the effects and risks of cannabinoids like THC and CBD are empirical matters answered by contemporary research, which is ongoing and complex. The two issues — how scheduling came to be, and what cannabinoids actually do biologically — are logically separate.