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Cannabis, also known as marijuana, is a psychoactive drug that comes from the cannabis plant. It is the most widely used drug in the world, with more than 200 million people using it in 2020. Cannabis use has risen steadily in the past two decades worldwide, but the drug is most popular in North America, Australia and New Zealand and West Africa.
Cannabis can make people feel happy, relaxed, giggly, hungry, tired, anxious or paranoid, and it has been used both recreationally and medicinally for thousands of years.
As the use of marijuana and its compounds rises around the world, New Scientist explores the latest research on the medical potential of cannabis, how it is grown and its environmental impact, the way cannabis affects our bodies and minds and what the marijuana of the future will look like.
The science of cannabis
Cannabinoids: THC, CBD and more
There are hundreds of active compounds in cannabis that contribute to its many and varied effects. Two are especially important: tetrahydrocannabinol, or THC, and cannabidiol, or CBD.
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THC is the main psychoactive element in cannabis and is what makes people feel high. It causes euphoria, hunger and, at high doses, anxiety or paranoia. Meanwhile, CBD doesn’t have psychoactive properties and may actually dampen THC’s effects.
Both THC and CBD belong to a group of chemicals known as cannabinoids. Our bodies naturally produce endogenous cannabinoids, or endocannabinoids, and we have receptors for these molecules in the brain, skin, lungs and other organs.
Medicinal potential
Cannabis has been touted as a treatment for a long list of conditions from cancer to post-traumatic stress disorder (PTSD). However, so far only four are backed by convincing scientific evidence: some kinds of chronic pain, muscle spasms from multiple sclerosis, nausea and vomiting caused by chemotherapy and seizures from two rare forms of epilepsy.
Other uses currently have little to no scientific backing. This is largely because cannabis is illegal in many countries, meaning researchers must obtain special permits and licences from the government to study its effects.
It may also partially be due to variations in dosages or methods of consumption, which can lead to inconsistent results across studies. There are hundreds of strains of marijuana, each of which differs in the amount of THC, CBD and other active compounds it contains.
There are also many ways of consuming cannabis. It can be smoked, vaporised, applied topically to the skin, eaten or turned into a tincture. This influences its effects. For example, the effects of smoked cannabis usually last around 1 to 4 hours whereas cannabis consumed in gummies, baked goods or other edibles, can last more than 6 hours. Meanwhile, topical applications usually don’t make people feel high and instead are used for pain management.
Side effects and addiction
No overdose deaths from cannabis have been reported. Still, the drug can cause adverse effects, including vomiting, paranoia, dry eyes and mouth, difficulty thinking and impaired movement. At high doses it could also lead to hallucinations and delusions.
Some studies suggest cannabis triggers psychotic episodes in people susceptible to schizophrenia or other mental health conditions, but so far only a correlation has been shown.
According to estimates from the US Centers for Disease Control and Prevention (CDC), about 30 per cent of people who use cannabis meet the criteria for addiction. Signs of cannabis abuse include an inability to quit the drug, withdrawal symptoms when stopping use and continued use despite it causing problems at work, school, home or in relationships.
