The 1961 Single Convention on Narcotic Drugs: How Cannabis Became a Controlled Substance Worldwide

The 1961 Single Convention on Narcotic Drugs is one of the founding documents of international drug control policy. Adopted under the auspices of the United Nations, it has profoundly influenced national laws regarding the production, trade, possession, and use of numerous substances, including cannabis.

To understand the history of global prohibition, it is essential to look back at the origins of this convention, its objectives, and its consequences.

Before 1961: The First International Conventions

The Origins of International Drug Control

In the early 20th century, several countries were concerned about the international trade in opium and other psychoactive substances. The 1912 International Opium Convention marked an important milestone in cooperation among nations. It did not yet regulate cannabis: the Hague Conference merely invited nations to study the issue of Indian hemp.

Other agreements followed, notably in 1925 and 1931, to establish controls over substances considered to pose a risk of abuse. These agreements laid the initial groundwork for an international monitoring system.

Cannabis entered international law with the Opium Convention of February 19, 1925, initiated by Egypt with the support of South Africa and Italy, among others. It restricted extracts and tinctures of Indian hemp to medical and scientific uses, but regulated only international trade: it did not prohibit either production or consumption. The 1931 Convention added the system of statistical estimates and classification by tables.

Why create a single agreement?

In the late 1950s, international rules were scattered across several treaties. The United Nations sought to simplify this framework and harmonize the obligations of states. The goal was to consolidate the main existing mechanisms into a single legal instrument.

The Single Convention on Narcotic Drugs was adopted in New York on March 30, 1961, following a conference held from January 24 to March 25, 1961. It entered into force on December 13, 1964, after the required forty ratifications.

The Treaty's Origins: Twenty Years of Negotiations (1948–1961)

The Single Convention was not originally drafted with cannabis in mind: it consolidates older treaties, and cannabis has become a point of contention along the way.

Three Projects, 1948–1958

In 1948, the Economic and Social Council (ECOSOC) adopted a resolution, drafted by the United States, calling for a single treaty to replace the conventions dating back to 1912. It had three objectives: to limit the production of raw materials, to codify existing texts, and to simplify the regulatory framework.

Three bills were introduced between 1950 and 1958. The bill from February 1950 proposed two options: to ban production except for scientific purposes, or to limit it to medical and scientific use under a state monopoly, with a temporary exception for countries where recreational use was traditional. Neither option was adopted. The 1958 draft included a section titled «Prohibition of Cannabis.».

A Controversial Medical Expert Opinion

In 1952, the WHO expert committee declared cannabis preparations to be «practically obsolete,» without providing any supporting evidence. The report by Pablo Osvaldo Wolff (1955), secretary of the committee, was presented to the Commission on Narcotic Drugs (CND) as the WHO’s position, even though the committee had not endorsed it, and the CND concluded that year that cannabis had no medicinal value. These assessments are those of the authors at TNI, a research center committed to drug policy reform.

The New York Conference (January 24 – March 25, 1961)

Delegates from 73 countries are meeting there. India, Pakistan, and Burma oppose the ban, with India in particular arguing for the bhang, a mildly intoxicating beverage. The definition of cannabis is limited to «flowering or fruiting tops»: leaves and seeds are excluded, which preserves traditional use. The phrase «other legitimate purposes» is rejected as contrary to the principle of limiting use to medical and scientific purposes. Cannabis is listed in Schedules I and IV, with a transitional provision in Article 49.

A Debate Among Historians

TNI describes a process led by the United States, with Harry Anslinger as a central figure. Collins qualifies this view: the United States is a key player but one that is often absent, and it is misleading to speak of a unified «prohibition regime.» He also notes that Washington has sought to weaken the 1961 Single Convention. These two interpretations coexist in the research.

What are the objectives of the 1961 Convention?

The text is based on a central principle: to restrict controlled substances to medical and scientific uses, subject to the specific provisions set forth in the treaty. In particular, it aims to regulate the cultivation, production, manufacture, trade, and distribution of certain substances.

The convention also provides for mechanisms for administrative oversight, reporting, and international cooperation. It contributes to the establishment of a common framework among the signatory states.

Why is cannabis an issue?

The Classification of Cannabis in International Schedules

The 1961 Convention classifies cannabis and its resin as substances subject to strict control. Originally, they were listed in both Schedule I and Schedule IV, the latter of which includes substances deemed the most dangerous and of «extremely limited» medical value, according to TNI. Schedule IV is in addition to Schedule I (Article 2, paragraph 5): according to TNI, it urges the Parties to consider banning even medical use; according to Collins, it leaves it up to each Party to decide whether or not to ban it. This classification reflects the prevailing scientific, political, and public health views at the time the treaty was adopted.

It also helps to curb the non-medical use of cannabis in many countries.

What the Text Really Says: Key Articles

Six articles are sufficient to understand the provisions on cannabis in the 1961 Convention. The quotations below are taken from a online version of the treaty ; the UNODC official text is considered authentic.

Collins also points out that there is still no accepted definition of «medical and scientific,» which he calls a legal loophole.

Is cannabis banned for all uses?

The 1961 Convention does not constitute an absolute ban on all cannabis-related activities. It provides for controlled medical and scientific use. A transitional provision (Article 49) also permitted non-medical use, which was to be phased out within twenty-five years, by 1989.

It also distinguishes between the cultivation of cannabis intended exclusively for industrial purposes—particularly for fiber and seeds—and crops subject to its main control regime. Article 28, paragraph 2, thus excludes cultivation intended exclusively for industrial or horticultural purposes. No THC threshold is specified therein.

How has the 1961 Convention influenced national laws?

States Parties must implement measures to ensure compliance with their international obligations. However, the specific procedures for sanctions and enforcement also depend on national legal systems.

In France, the law of December 31, 1970, is part of this international trend, while also addressing political and public health concerns specific to the country. To learn more, read our article on the’The History of Cannabis Prohibition in France and the 1970 Law. The convention also influences the policies adopted in many other European, American, African, and Asian countries.

It thus helps to establish a relatively uniform global framework, even though its implementation varies from country to country.

The system's bodies: CND, INCB, WHO

Three institutions are involved in cannabis policy, and their roles are distinct: the WHO assesses, the CND decides, and the INCB monitors implementation.

The INCB issues findings and recommendations; it does not have the authority to impose sanctions directly.

Has the 1961 Convention evolved?

The 1972 Protocol

A protocol signed on March 25, 1972, amends the Single Convention to strengthen certain control and cooperation mechanisms. It also emphasizes measures for treatment, rehabilitation, and social reintegration. It entered into force on August 8, 1975. France has been a party to the amended text since September 4, 1975, and the convention has 186 parties.

The 1971 and 1988 Conventions

The 1961 Convention is supplemented by two other instruments, and it is important to understand how they relate to one another, since the debate over personal use is primarily addressed in the latter.

• 1971 Convention on Psychotropic Substances. It classifies THC under Schedule II. In 2020, the CND rejected the transfer of THC and dronabinol to the 1961 Convention.
• 1988 Convention Against Illicit Trafficking. Its two major contributions are the control of chemical precursors and the focus on traffickers. Article 3 addresses personal use that is «contrary» to the 1961 and 1971 conventions; the official commentary describes it as a controversial issue and a compromise, with a constitutional safeguard clause and wording that allows each Party to interpret the preceding provisions (Collins, 2020).

For a French reader, the lesson is this: the treaties require that trafficking be controlled and punished, but leave States some leeway regarding the treatment of users. The 1970 law is therefore a national choice, not a clear international obligation. This conclusion stems from Collins’s interpretation; it is contested by those who interpret Article 4 of the 1961 Convention more strictly.

The Reclassification of Cannabis in 2020

On December 2, 2020, the The United Nations Commission on Narcotic Drugs has removed cannabis and its resin from Schedule IV of the 1961 Convention, by a vote of 27 to 25, with one abstention, out of 53 members. This decision recognizes the need to take greater account of the potential medical uses of cannabis. Cannabis remains listed in Schedule I and continues to be subject to international controls.

The vote, recommendation by recommendation

The vote concerned several WHO recommendations from 2019. According to the results reviewed, only one was adopted.

The United States voted in favor, Russia voted against; Hungary is the only European Union member state to have voted against Recommendation 5.1.

What This Changes—and What It Doesn't

The WHO determined that the listing in Schedule IV «is not consistent with the criteria» for that schedule, citing the benefits of cannabis for pain, nausea, and epilepsy, while acknowledging that the therapeutic evidence is limited. The delisting may facilitate medical research.

The U.S. State Department clarified that the vote «is not an endorsement of the use of the cannabis plant or cannabis resin for medical purposes,» and that each country remains free to set its own policy. Article 4, paragraph (c), continues to limit use to medical and scientific purposes.

Do modern legalizations call the Convention into question?

Since the 2010s, several countries have adopted regulations authorizing certain non-medical uses of cannabis. These developments raise questions about how new national laws relate to international obligations. Some countries favor strictly regulated models, while others maintain a policy of prohibition.

These legalizations are exacerbating a real legal conflict, but experts disagree on its nature and how to resolve it. Here are the main positions, along with their proponents.

Three caveats are in order. Walsh and Jelsma are researchers committed to reform, and their text is a political commentary rather than a neutral legal study. TNI, which publishes their critique of High compliance, takes the same approach. Finally, the INCB is the body responsible for monitoring the implementation of the treaties, which explains its strict interpretation.

One point tempers the debate: according to Walsh and Jelsma, the treaties allow room for decriminalization or for the implementation of harm-reduction policies. Legalizing a non-medical market and decriminalizing use are therefore two legally distinct matters.

The 1961 Convention thus remains at the center of discussions on the future of international drug control.

Conclusion: An Essential Read for Understanding Cannabis Legislation

The 1961 Single Convention on Narcotic Drugs played a decisive role in the history of prohibition. By harmonizing international regulations, it helped shape national cannabis control policies.

Despite scientific and legislative developments, this treaty remains a key reference for understanding the legal issues involved in global regulation.

FAQ – 1961 Convention

When was the Single Convention on Narcotic Drugs signed?

It was adopted in New York on March 30, 1961, and entered into force on December 13, 1964.

Does the 1961 Convention prohibit medical cannabis?

No. It provides for medical and scientific uses that are subject to strict regulation.

Was cannabis removed from international schedules in 2020?

It has been removed from Schedule IV but remains listed on Schedule I.

Does the 1961 Convention apply to industrial hemp?

Crops grown exclusively for fiber or seeds are specifically exempt from the provisions of Article 28.

Does the 1961 Convention require countries to criminalize personal use?

Not clearly. Article 36 allows for some flexibility, offering alternatives to punishment such as treatment or rehabilitation. The issue is primarily addressed in the 1988 Convention (Article 3), whose wording allows each State to interpret the preceding provisions.

Did the 2020 vote legalize cannabis?

No. Removing it from Schedule IV may facilitate medical research, but it does not legalize recreational use, which remains restricted by Article 4, paragraph (c), of the Convention.

Do the legalizations in Uruguay, Canada, or Germany comply with the Convention?

The INCB believes not. Some legal scholars, on the other hand, argue that there is room for interpretation, and several states acknowledge a conflict with the treaties. There is no international court with the authority to rule on the matter.

Bibliography

Texts and Institutional Sources

• UN Treaty Collection, Single Convention on Narcotic Drugs of 1961, as amended by the 1972 Protocol (Status of the parties, dates of signature and entry into force).
• UN Info, article on Uruguayan law and the INCB's position.
• ANSM, Responses Regarding the Medical Cannabis Pilot Program (THC threshold of 0.3 %).

Articles and Research Papers

• Collins, A Brief History of Cannabis and the Drug Conventions, Cambridge University Press, 2020.
• Walsh and Jelsma, article on legal options in response to legalization, 2019.
• TNI, The Rise and Decline of Cannabis Prohibition, Chapter 1 (source of advocacy for reform).
• TNI, A House of Cards, 2022 (source of advocacy for reform).
• Swaps Nos. 96–97, Special Report on the 50th Anniversary of the 1970 Law.

Press

• NPR, «U.N. Commission Removes Cannabis From Its Strictest Drug Control List», December 2, 2020.
• The Paper, «A UN board says legalization violates treaties», March 2024.
• Ilesol, Analysis of the CND Vote (figures are for illustrative purposes only).

See also on Newsweed

• History of Cannabis Prohibition in France: The 1970 Law