Reviewed and updated: August 2026
THC acts on cannabinoid receptors in the brain and can temporarily change mood, perception, memory, attention, coordination and reaction time. Risk is higher with frequent use, high-THC products and use beginning during adolescence. Cannabis can cause anxiety or paranoia and, rarely, a psychotic episode. Effects vary, and CBD is not a guarantee against harm.
What does cannabis do to the brain?
THC can activate CB1 cannabinoid receptors, which are abundant in the central nervous system. This changes signalling involved in learning, memory, reward, movement, appetite and other functions. The immediate result may include euphoria and relaxation, but also slower reaction time, altered time perception, impaired coordination, anxiety or confusion.
Can cannabis affect memory?
Yes. During intoxication, cannabis can make it harder to learn, retain new information, concentrate and make decisions. These short-term effects are especially relevant at school, work and while driving.
Frequent use over months or years is associated with greater cognitive risk, particularly when use starts young. Individual outcomes differ, and research cannot reduce every effect to one simple rule about permanent or reversible change.
Can cannabis affect mental health?
Cannabis can cause anxiety, panic or paranoia. Rarely, it can trigger a psychotic episode involving hallucinations, extreme confusion or loss of contact with reality. Frequent long-term THC use is associated with an increased risk of developing or worsening anxiety and depression-related disorders. Higher-THC products can further increase mental-health risks.
People with a personal or family history of psychosis, schizophrenia or other serious mental-health conditions should speak with a healthcare professional and may be at greater risk.
How does cannabis affect teenagers and the developing brain?
The brain continues developing into the mid-20s. Health Canada advises that adolescents are more vulnerable to cannabis-related harms. Earlier initiation and frequent use increase the likelihood of problems with memory, attention, learning, educational outcomes, mental health and cannabis use disorder.
The lowest-risk choice for teenagers is not to use cannabis. Adults should store cannabis securely and never provide it to minors.
Does cannabis make you tired?
It can. Drowsiness is a recognized immediate effect, and some lingering effects can last into the next day. Product type, dose, tolerance, other substances and individual response all matter. Feeling awake does not prove that attention, judgment or reaction time have returned to normal.
When should someone get medical help?
Seek urgent help for severe confusion, hallucinations, chest pain, seizures, loss of consciousness, trouble breathing or symptoms that feel dangerous. In Canada, call 911 for an emergency or contact the provincial poison centre.
Frequently asked questions
Does CBD affect the brain?
Yes. CBD is not intoxicating, but Health Canada notes that it can still affect the brain.
Can cannabis cause paranoia?
Yes, particularly with larger doses or high-THC products and in susceptible people.
Is it safe to drive once the high feels gone?
Not necessarily. Impairment can outlast noticeable intoxication and may persist for more than 24 hours in some situations.
Primary sources: Health Canada, “Cannabis and your health”; Health Canada, “Cannabis impairment and safety risk”; Health Canada, youth cannabis facts.
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