Effects of cannabis

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 also pose risks and have adverse effects on your health.

The main attraction of non-medical cannabis use is the high—a kind of euphoria—mainly 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.

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. When cannabis is consumed in edible forms, the effect takes longer to appear and lasts longer.

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

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., dried cannabis, 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

Cannabis : effets psychoactifs (in French only) 
Institut national de santé publique du Québec