How it Affects You

Using cannabis disrupts the central nervous system, affecting how people who use it function and what they can do. Cannabis isn’t harmless, and it’s not just something else that’s out there. Using cannabis can be dangerous and have adverse effects on your health.

“High” then “stoned”

The main attraction of non-medical cannabis use is the high—a kind of euphoria—caused by the THC. Occasional users tend to experience the main effects in two successive phases:

  • Phase 1, the high, beginning within minutes of inhalation or about an hour after ingestion:
    • Euphoria—a sense of satisfaction and well-being
    • Carefree mood
    • Increased sociability
    • Heightened experience of the senses
    • Impression of being more creative
    • Spontaneous laughter
  • Phase 2, being stoned, generally begins an hour or more after inhalation or six hours or more after ingestion:
    • Lethargy, slowed physical and mental functioning. This is caused by the elimination of THC from the body.

Effects on cognitive function

Cognitive function may be affected in both phases—high and stoned. Cognitive functions are those that depend on the brain, allowing us to communicate, perceive our surroundings, concentrate, remember, and learn. A person under the influence of cannabis might therefore experience the following:

  • Disruption of
    • Short- and medium-term memory
    • Attentiveness
    • Concentration
  • Impaired judgement
  • Slower reaction time

Inhalation of cannabis smoke or vapour affects cognitive abilities very rapidly. The effect peaks in roughly 30 minutes and generally takes less than six hours to fade. Other ways of using cannabis tend to have longer-lasting but more limited effects on cognitive functioning.

A key aspect of short-term cognitive impairments is how they increase the risk of accidents if the person tries to drive.

The law of effect

The experience of using a drug is influenced by many factors—the user’s physiology and mood, the substance used, and the context they use it in. These things combine together into associations that are subject to the law of effect.

The effects of cannabis vary enormously from one user to the next, in response to external parameters such as

  • The form used (e.g., marijuana, hashish, dabs)
  • The dose taken
  • The concentrations of THC and CBD in the preparation used
  • The method of administration (i.e., inhalation or ingestion)
  • The user’s experience
  • The user’s physical and mental state
  • Social context (e.g., alone at home, with others at a party)
  • Alcohol, other drugs, or medications used with cannabis, which can amplify the effects


BEN AMAR, Mohamed. Drogues: savoir plus/risquer moins - le livre d’information. Centre québécois de lutte aux dépendances, 7e édition, Montréal, Québec, Canada, 2014, 262 p. (in French only)

BROYD, Samantha J. et al. Acute and Chronic Effects of Cannabinoids on Human Cognition —A Systematic Review. Biological Psychiatry, vol. 79, no 7, 2016, p. 557-567.

VOLKOW, Nora D. et al. Adverse Health Effects of Marijuana Use. The New England Journal of Medicine, vol. 370, no 23, 2014, p. 2219-2227.

Last update: February 26, 2021 3:14 PM