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Drugs are divided into four main categories: cannabis, opiates, central stimulants and hallucinogens. Of these, cannabis is the most common drug of use amongst young people after alcohol. Cannabis is therefore the main focus of this page.

Cannabis user gets poor study-outcome!

This was shown in a study where the focus was on association between the maximum frequency of cannabis use before age 17 years (never, less than monthly, monthly or more, weekly or more, or daily) and seven developmental outcomes assessed up to age 30 years (high-school completion, attainment of university degree, cannabis dependence, use of other illicit drugs, suicide attempt, depression, and welfare dependence).

E. Silins et al. recorded clear and consistent associations and dose-response relations between the frequency of adolescent cannabis use and all adverse young adult outcomes. After covariate adjustment, compared with individuals who had never used cannabis, those who were daily users before age 17 years had clear reductions in the odds of high-school completion and degree attainment, and substantially increased odds of later cannabis dependence, use of other illicit drugs, and suicide attempt.

The Lancet Psychiatry. 2014;1(4):286-93.

Different categories of drugs

Drugs fall into four main categories: cannabis (marijuana and hash), opiates (opium, morphine, codeine, heroin and methadone), central stimulants (khat, cocaine and amphetamine) and hallucinogens (ecstasy, LSD, mushrooms, etc.). Of these, cannabis is the one that is the most common amongst young adults. Find out more about specific drugs on The Swedish Council for Information on Alcohol and Other Drugs (CAN).

Some figures...

Most young people have never used drugs; however, some 35 per cent of male students and 33 per cent of female students studying full-time at university level (between the ages of 18 and 34) have done so at one time or other. The proportion of drug-takers is higher (for both sexes) amongst students on free-standing courses than amongst students on full study programmes. For women, drug use tends to rise in proportion to length of study - a relationship that doesn't seem to apply to drug use by men. Nor is there any overall difference between students who have taken more or less than 50 per cent of their credits. The use of sedatives or painkillers is roughly as common amongst male and female students, four per cent of whom have used drugs of this kind at some time in their life without a doctor's prescription.

About cannabis

Cannabis use increased around Europe between 1995 and 2003, since when in most countries it has either levelled off or gone into decline. In the past year, Sweden saw a relatively low level of cannabis use in the 15 to 24 age-group.

A heated liberalisation debate about cannabis is currently taking place, with the pro camp making a great many claims about its supposed harmlessness - an attitude that in being disseminated quickly and effectively by the net has taken root amongst teenagers and young adults. There are a great many false claims on the internet and it can be difficult to know what and who to believe. Because of this, we include here an informative text on cannabis based on the latest research. Sources and tips for further reading are at the bottom of the page.

If you or a fellow student are abusing cannabis, please feel free to contact the Student Health Service for a chat. You can also turn to Maria Beroendecentrum for help.

Facts about cannabis

Cannabis is by far the most common first-use drug amongst young people. According to the statistics, six per cent of young Swedes (15 to 24 years old) have smoked cannabis over a twelve-month period, which can be compared with an average of almost 16 per cent for Europe (ECNN, 2009), making its rate of use amongst young Swedes one of the lowest in the continent.

Marijuana is the dried leaves and buds of the Cannabis Sativa plant, while hash is the resin extracted from the same plant. The substance THC (delta-9-tetrahydrocannabinol) in the plant is the main agent of both the high and low of cannabis use. While the concentration of THC in the drug varies greatly, it has increased over the past few decades.

THC binds to receptors for endogenous cannabis-like substances in the brain such as anandamide, its euphoric effect coming from the activation of the dopamine pathways of the limbic system via different neuronal reconnections and certain opiate receptors.

Harmful effects

Many studies have been done on the harmful effects of the drug, but since THC concentrations vary, so do the results.

The risk of dependency is rated differently by different studies. About ten per cent of occasional cannabis smokers seem to develop a dependency at some time in their lives, the earlier the debut, the greater the likelihood. This, in turn, increases the risk that users will graduate to other illegal drugs, start to perform poorly in their studies, and develop psychotic symptoms.

Cognitive functions, such as attention, concentration ability and memory can be damaged, which affects the development of identity. These disorders persist after the use of cannabis has ceased and can retard development. A damaged short-term memory can also cause problems with learning and relationships, and make it harder for people to make realistic appraisals of their surroundings.

Ever since cannabis became popular in the 1960s, there have been studies suggesting that the drug can also cause mental disease, and there is now growing consensus in the scientific community on the strong links between cannabis and serious mental ill-health. Even when controlling for individuals who have "self-medicated" after experiencing nascent psychiatric problems, there is reason to believe that cannabis is an immediate trigger of severe acute psychoses (so-called toxic psychosis) or even schizophrenia. Acute cannabis-induced psychoses usually require hospitalisation, after which the long-term prognosis will partly depend on underlying determinants.

It's difficult to give any hard and fast facts about how common toxic psychosis actually is, but it has been estimated that one in ten cannabis smokers risk suffering a psychotic episode at some time in their lives, more so if the THC concentration in the drug is high. A cannabis high can also give rise to panic attacks, especially in people who are unaccustomed to the drug or the THC concentration in the smoke. There is also a direct causal link between intensive and prolonged cannabis use and depression. Already extant depressive problems are usually exacerbated when sufferers start to smoke cannabis, and there is, as mentioned above, an association between cannabis smoking and schizophrenia - even though there is no evidence of any causal relationship between the condition and the drug per se.

Finally, habitual cannabis abuse during pregnancy causes low birth weight and is thought to damage the baby's central nervous system.

Signs of cannabis use

The immediate symptoms are similar to alcohol intoxication. Bloodshot eyes, dryness of the mouth, a tendency to lose the thread of a conversation. The high usually induces a sense of mild elation, gaiety and prolonged bursts of laughter. This then wears off to be replaced by growing introspection, broodiness and somnolence (the person is extremely tired but responsive).

Cannabis is fat soluble and is secreted slowly from the body, with a "half life" of about 60 hours. This means that if you smoke a couple of times a week, you are never completely drug free. The drug is gradually stored primarily in the fat-rich brain, and after a period of regular use many smokers report experiencing a more or less continual high. Never being drug-free and the high degree of fat-solubility precipitates dependency.


Contrary to what many people think, the withdrawal symptoms of cannabis are pronounced, making it difficult for people to quit. Initially, withdrawal is experienced as an urge to "roll up", but after four or five days, the irritation and restlessness gradually escalate into a state of psychomotor agitation. Often the irritation escalates into extreme irascibility. After a week or so, vegetative symptoms start to appear, such as perspiration from unusual parts of the body like the palms, back and scalp. Insomnia sets in, and any sleep obtained can often bring vivid, distressing dreams. Some individuals at this stage can also develop delusions, hallucinations and confusion. These symptoms start to wear off after a fortnight or so, and remain for about a week. Following this is a craving for the drug that persists for months, sometimes years.

Cannabis as a medicine

Cannabinoids have long been the subject of medical research. While scientists have been looking into its therapeutic uses for MS-related muscular rigidity, the prevention of prostate cancer, glaucoma and loss of appetite caused by chemotherapy, the only cannabinoid medicine widely available on the European market was a prescription drug for obesity and related problems called Acomplia (Rimonabant); however, the drug was later banned for its serious adverse effects on the mental health of users.

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