Of all the plants cultivated by humans, none has been the subject of as much praise and criticism as cannabis. A passionate debate pits proponents of its therapeutic virtues against detractors who point out its health risks.
Based on the most recent scientific evidence, I will answer these two questions:
Is cannabis a medicinal plant?
Undoubtedly, yes .
The Emperor of China, Shen Nung , was the first to discover the therapeutic properties of cannabis, describing them in his compendium of medicinal herbs, the Shen Nung Pen Ts ‘ year Ching , written in 2737 BC.
In 1833, Sir William Brooke O’ Shaugnessy , an Irish physician and surgeon, while treating his patients in India, discovered the analgesic (against pain), antiemetic (against nausea and vomiting), anticonvulsant (against epilepsy), appetite stimulant and muscle relaxant properties of the herb.
In 1839, Dr. O’Shaugnessy published his observations, which led to the rapid expansion of medicinal cannabis use throughout the world.
In 1851, cannabis was included in the third edition of the United States Pharmacopoeia, granting it legitimate medicinal status. The American Pharmacopoeia recommended its use as an analgesic, antiepileptic, and hypnotic (to promote sleep).
Since 1851, liquid extracts and tinctures of cannabis have been marketed by the pharmaceutical companies Bristol-Myers Squibb, Burroughs- Wellcome , Eli Lilly, Merck, and Park-Davis. They are sold in all pharmacies and without a prescription.
Cannabis was also included in the British Pharmacopoeia until 1971, when its medicinal use was suspended following the adoption of the United Nations Convention on Psychotropic Substances.
As of September 18, 2025, 453 controlled clinical trials evaluating the efficacy and safety of cannabis and cannabinoids in 39 diseases have been published worldwide.
These clinical trials are called controlled trials because they compare the efficacy of cannabis and cannabinoids with medications already on the market or with a placebo. They allow conclusions to be drawn based on statistical analysis and were conducted on a total of 29,711 patients.
As of September 18, 2025, 78 countries have legalized the medicinal use of cannabis, of which 46 (59%) dispense it in pharmacies.
Is cannabis a dangerous drug?
Undoubtedly, yes, in people who consume it in high doses or if it is smoked by people under 25 years of age.
Cannabis is not harmless and its undesirable effects must be emphasized, particularly in adolescents.
Recreational cannabis users sometimes consume significant amounts of cannabis in search of pleasurable sensations such as euphoria, i.e., a feeling of well-being and satisfaction.
Recreational cannabis use produces a toxic picture that includes different undesirable effects, both acute (short-term) and chronic (long-term).
The most important acute effects are cognitive disorders, including problems with memory, attention, concentration, and balance.
The chronic effects of cannabis are significant. The most serious is that consuming large amounts can eventually lead to the development of various forms of psychosis, including schizophrenia.
Furthermore, it must be emphasized that the human brain does not fully develop until the age of 25. Therefore, young people under 25 are also at risk of developing psychosis later if they start using cannabis early and continue to use it until the age of 25.
CONCLUSIONS
It is important to distinguish the medicinal use of cannabis from its recreational use.
Cannabis and cannabinoids have produced significant and conclusive therapeutic effects for a dozen diseases. Medical cannabis is currently legalized in 78 countries, of which 46 (59%) sell it in pharmacies.
In its therapeutic use for various diseases, a small amount of full- spectrum cannabis or cannabinoids is sufficient in most cases to control the symptoms of the diseases being treated.
However, significant amounts of cannabis can be consumed during recreational use, which makes cannabis considered a dangerous drug in this case.
REFERENCES
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- BEN AMAR M ( 2024 ). Therapeutic potential of cannabis and cannabinoids : laws and regulations in force in Canada . In: Integrated Approach to Cannabis Use: Research, Prevention, and Treatment. Under the direction of Manuel Isorna Folgar, Francisco Fariña Rivera, Francisco Salvador Pascual Pastor, and Jaime Fraga Ares. Madrid, Dykinson, pp. 169–178.
- BEN AMAR M ( 2022 ). Medicinal uses of cannabis and cannabinoids. Analysis of all controlled clinical trials conducted worldwide. Bilbao, EDEX Foundation, 333 p.
- BEN AMAR M (2020 ). Cannabis and psychosis : A review of the risk factors involved . American Journal of Plants Sciences , vol. 11, no. 12, p.1949-1990.
- BEN AMAR M (2018). Le Cannabis: Pharmacology et Toxicologie . Montreal, Center Québécois de Lutte aux Dependencies (CQLD), 511 p.
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- NATIONAL ACADEMIES OF SCIENCES, ENGINEERING, AND MEDICINE (2017). Part II : Therapeutic effects . Chapter 4 : Therapeutic effects of cannabis and cannabinoids . In : The Health Effects of Cannabis and Cannabinoids . The Current State of Evidence and Recommendations for Research . Washington DC, The National Academies Press , p. 4-1 to 4-43.
- O’ SHAUGNESSY WB (1838-1840). on the preparation of the Indian hemp , or gunjah (Cannabis sativa ): their effects on the animal system , in health , and their utility in the treatment of tetanus and other convulsive disorders . Transactions of Medical and Physical Society of Bengal , p. 421-461.
- RUSSO E (2003 ). Cannabis. From Pariah to Prescription . Binghampton , The Haworth Integrative Health Press , 187 p.
- UNITED STATES PHARMACOPEIA (1851 ). Extractum cannabis . Extract of hemp . An alcoholic extract of the dried tops of Cannabis sativa- variety Indica. United States Pharmacopeia . Third edition .
- WIKIPEDIA (2025). Medical cannabis. September 18, 2025,15 p
Professor Mohamed BEN AMAR
Pharmacologist
University of Montreal
