WHO-study International Co-operation

Current WHO Study on Cannabis Use - The health and social effects of nonmedical use

An international group of experts chaired by Sweden’s Minister of Health and Social Affairs met in April 2015 to share the results of research into the health effects of cannabis use – covering both mental health and overall health.

The focus was on the health and social effects caused by the nonmedical use of cannabis, especially in young persons and long-term users.

This study sums up the recent findings from many international researchers and details the health impacts of regular nonmedical cannabis use on, for instance, the human brain and airways.

General information:

  • 2014: Globally, 181.8 million people aged between 15 and 64 years used cannabis for nonmedical reasons, 13.1 million individuals are estimated to be dependent.
  • In the industrialised nations, use rates are disproportionately higher than in the so-called developing countries
  • Of the cannabinoids contained in the female cannabis plant, at least 750 compounds produce chemical effects and 104 produce other effects. The most widely known substance is THC (“Delta-9-Tetrahydrocannabinol“) that is primarily responsible for the psychoactive effects cannabis produces.
  • The most common type of cannabis use is the smoking of marijuana. Another, increasingly popular form of use is vaporisation. Both ways of administration involve very high blood levels of THC that peak after 15—20 minutes and drop off after about two to three hours.
  • In recent years, several European countries and US states have noted massive increases in the THC contents of cannabis as a result of specifically bred plant strains, up from about three per cent to 16 per cent or more.

Risk groups and protective factors:

  • The WHO study found that males with rather moderate academic success, early school leaving, as well as poor parenting experiences are primarily at risk.
  • By contrast, a functioning family environment, especially parental support in puberty, is a predictor of abstinence to drugs in general and cannabis, in particular. Religious involvement and academic success are also linked to abstinence.

Short-term effects:

  • Cannabis can cause panic attacks, episodes of euphoria, hallucinations and nausea
  • Impaired consciousness, behaviour and perception, slower response speed have been reported
  • The last WHO study of 1997 had not been able to verify the association between a higher accident risk and cannabis use while current epidemiological studies demonstrate that drivers under the influence double their accident risk.

Long-term effects:

  • Cannabis can cause dependence. First-time cannabis users have a 1:10 risk of developing dependence, daily users have a risk of 1:3.
  • Evidence-based adverse effects are social withdrawal, depression, psychosis /hallucination, generalised dysphoric effects, heightened suicidality and cancer risks as well as chronic-obstructive bronchitis / pulmonary disease
  • The adverse effects of regular cannabis use and the resulting addiction risk are far more pronounced in adolescents (14-16 years) than in adults.
  • Moreover, long-term use also irreversibly impairs both memory and IQ, as shown in a study out of New Zealand. In addition, MRI studies proved changes in the brain structure.    
  • Some studies have demonstrated a link between a higher risk of myocardial infarction and stroke at a young age and long-term cannabis use.
  • Moreover, the death rate, too, is multiple times higher in long-term users than in abstinent persons.