When cannabis is smoked, THC and other chemicals in the plant pass from the lungs into the bloodstream, which rapidly carries them throughout the body to the brain. The person begins to experience effects almost immediately. Many people experience a pleasant euphoria and sense of relaxation. Other common effects, which may vary dramatically among different people, include heightened sensory perception (e.g., brighter colors), laughter, altered perception of time, and increased appetite.

If cannabis is consumed in foods or beverages, these effects are somewhat delayed—usually appearing after 30 minutes to 1 hour, because the drug must first pass through the digestive system. Eating or drinking cannabis delivers significantly less THC into the bloodstream than smoking an equivalent amount of the plant. Because of the delayed effects, people may inadvertently consume more THC than they intend to.

Pleasant experiences with cannabis are by no means universal. Instead of relaxation and euphoria, some people experience anxiety, fear, distrust, or panic. These effects are more common when a person takes too much, the cannabis has an unexpectedly high potency, or the person is inexperienced. People who have taken large doses of cannabis may experience an acute psychosis, which includes hallucinations, delusions, and a loss of the sense of personal identity. These unpleasant but temporary reactions are distinct from longer-lasting psychotic disorders, such as schizophrenia, that may be associated with the use of cannabis in vulnerable individuals.

Although detectable amounts of THC may remain in the body for days or even weeks after use, the noticeable effects of smoked cannabis generally last from 1 to 3 hours, and those of cannabis consumed in food or drink may last for many hours.