Medical Cannabis: Science, Research and Risks

What "medical cannabis" covers

The phrase is used for several different things. It can mean the dried flower or an oil made from the plant, prescribed or recommended within a national programme. It can mean a purified single compound such as cannabidiol (CBD). And it can mean a licensed medicine that contains a cannabinoid, such as a purified CBD solution approved for certain rare seizure syndromes, or synthetic THC-type capsules prescribed for nausea during cancer treatment.

These are not interchangeable. A product with a defined dose, made to pharmaceutical standards and tested in trials, tells you something quite different from a plant product whose content varies from one batch to the next. When a claim about cannabis is read, the first question is always which product it was about.

What the research can and cannot show

Good evidence comes from randomised trials that compare a defined product with a placebo or another treatment, and from systematic reviews that pool several of them. For a few conditions, the best-supported findings concern specific licensed cannabinoid medicines rather than the plant in general. For many other conditions the trials are small, short, use different products and doses, or measure different outcomes, so they cannot be added up into a firm answer.

Surveys, patient testimonies and laboratory studies on cells or animals are useful for generating questions, but they cannot show that a treatment works in people. Reading a study means checking who took part, how long it lasted, what was compared and who paid for it.

Risks to weigh first

THC, the compound that produces the high, impairs attention, reaction time and coordination, which is why driving or operating machinery after use is dangerous. In some people, especially with high-THC products, heavy use and use that starts young, it can bring on anxiety or psychotic symptoms, and regular use can lead to dependence, known as cannabis use disorder.

Cannabinoids can interact with other medicines. CBD in particular can change how the liver handles some drugs, including certain anticonvulsants and blood thinners, and cannabis can add to the sedation caused by alcohol, sleeping tablets or opioids. Smoked cannabis carries the harms of inhaling smoke. Edible products are easy for children to swallow by accident and are slow to act, which leads adults to take more than they intended.

Cannabis use is generally advised against during pregnancy and breastfeeding. Anyone with a history of psychosis, serious heart disease or substance use problems should talk to a clinician before using it at all.

Where to read primary sources

For product and safety information, start with the regulator that covers your country, such as Health Canada, the US Food and Drug Administration or the European Medicines Agency. For evidence, look for systematic reviews in peer-reviewed journals and for the trial registries where studies are listed before they report. A pharmacist can check a cannabinoid product against everything else you take.