Cannabis

Where the substance comes from

Cannabis comes from hemp grown outdoors in warm countries and, increasingly, under lamps in indoor operations close to the consumer. Herbal cannabis is the dried flower; resin is made by pressing trichome powder. A growing share of the European market no longer comes from Morocco but from local cultivation, which has pushed up the average tetrahydrocannabinol (THC) content: rarely above 8 % in the 1990s, it is now often 15 to 25 % for herb and can exceed 30 % for some resins. Concentrated extracts (oils, wax, shatter) go far higher.

A little history

Hemp was domesticated in Central Asia, for its fibre and seeds, more than ten thousand years ago. The oldest evidence of its psychoactive use comes from 2,500-year-old braziers found in a cemetery in the Pamirs, in western China, in which THC-rich cannabis was burned. Hashish spread through the Muslim world from the twelfth century; in India, bhang has accompanied religious festivals for centuries.

European medicine discovered it through William O'Shaughnessy, a physician of the East India Company, who brought it back in 1839; the Club des Hachichins gathered Moreau de Tours, Baudelaire and Gautier in Paris in 1844. Cannabis tinctures appeared in pharmacopoeias until the 1930s. Then the wind turned: the 1925 Geneva convention listed it among narcotics, the United States taxed it into prohibition in 1937, and the 1961 Single Convention imposed prohibition on the whole world.

THC was only isolated in 1964 by Raphael Mechoulam in Jerusalem, and the receptors it acts on, the endocannabinoid system, were discovered between 1988 and 1992. The Netherlands has tolerated coffee shops since 1976; Uruguay legalised in 2013, Canada in 2018, Germany in 2024, and a number of American states since 2012, while the THC content of what is sold has tripled in twenty years.

The forms it takes

• Herb, smoked in a rolled cigarette, often mixed with tobacco — which adds nicotine dependence to THC dependence.
• Resin, heated then crumbled. It is the form most often adulterated: wax, paraffin, henna, dyes, sometimes lead.
• Edibles (cakes, sweets, gummies). The effect takes one to three hours to build, which prompts a second dose before the first has worked: this is the commonest cause of acute poisoning in first-time users and in children who swallow them by accident.
• Vape cartridges and concentrates, heavily dosed, delivering in one puff the equivalent of several cannabis cigarettes.
• Products sold as “CBD”, legal in many countries but sometimes containing something else entirely: see the page on synthetic cannabinoids.

What the user is looking for

Relaxation, loss of inhibition, a sense that time is slowing, appetite, sociability, sometimes helpless laughter. In some people, sedation sought as a way to sleep or to quiet anxiety. It is precisely that “medicine” use that installs dependence most reliably: the substance becomes the only available answer to an uncomfortable inner state.

Immediate unwanted effects

• Dry mouth, red eyes, racing heart, blood pressure dropping on standing.
• Impaired coordination and distance judgement: road accident risk multiplies, and far more so when alcohol is added.
• Loss of immediate memory, difficulty following a conversation or a lesson.
• Acute panic, a sense of impending death, sometimes persecutory ideas: a bad trip is not reserved for heavy doses and often happens to the occasional user.
• Repeated, intractable vomiting in long-term daily users, relieved only by very hot showers: cannabinoid hyperemesis syndrome, long unrecognised.

Medium and long-term risks

The main risk is not fatal overdose — none is described for cannabis alone — but the quiet arrival of three things. First dependence: roughly one user in ten, and close to one in six where use began in adolescence. Then educational or occupational drift, through loss of working memory and motivation, which corrects slowly after stopping. Finally psychotic risk: cannabis does not create schizophrenia but brings forward its age of onset and triggers episodes in predisposed people, the more so as the product is strong and the use early and daily.

Smoked with tobacco, it adds every tobacco risk: chronic bronchitis, cancers of the airway, cardiovascular disease. Burning a joint exposes the lungs to more tar than a cigarette, because it is inhaled more deeply and without a filter.

How to spot use

• A characteristic smell on clothes and in the bedroom, excessive air freshener or incense.
• Red eyes and unexplained “redness relief” eye drops.
• Rolling papers, card filters, a grinder, numerous lighters, precision scales.
• Night-time hunger, shifted sleep, very hard mornings.
• Falling school results, abandoned activities that used to matter, an abrupt change of friends.

Analytically, THC is detectable in urine for about three days after a single use, one to two weeks in a regular user and up to a month or more in a long-term daily user, because it is stored in fat. In blood the window is far shorter, from a few hours to a day or two. A positive test therefore never proves recent use.

Why the effect is stronger in adolescents

The brain finishes maturing around twenty-five, and the prefrontal cortex — impulse control, planning, attention — is served last. The endocannabinoid system plays a direct part in that pruning of neural connections. Regular exposure during this period therefore does not do what it does in an adult: dependence installs faster, the effect on memory and learning is more marked, and it persists for weeks after stopping. At the same dose, in a lighter body, the concentration reached is also higher. That is true of every psychoactive substance, legal ones included: one can of energy drink gives a 45 kg adolescent twice the caffeine dose per kilogram that it gives an adult.