Effects of Marijuana

Marijuana is a combination of shredded leaves, stems and flower buds of the Cannabis sativa plant. In a 2010 survey, 17.4 million people in the United States said they had used marijuana in the past month. The National Institute on Drug Abuse says marijuana is the most commonly used illegal drug.

marijuana smoker
Smoking marijuana produces euphoria and a range of psychological and physical effects that can be unpredictable at times.
Credit: Igor Kolos | Shutterstock

Marijuana is usually smoked, but it can also be eaten, mixed with food or brewed as a tea. In general, smoking marijuana will trigger effects faster and more predictably than ingesting marijuana. Smoking marijuana will cause psychological effects within 30 to 60 minutes as the psychoactive chemical THC is absorbed into the blood through the lungs and circulated around the body. It takes two to three hours after ingesting marijuana for effects to appear, and these may last slightly longer: up to three hours for smoking and up to four hours if marijuana was eaten.

Marijuana can impair thinking, memory and learning for weeks after use. It produces a range of psychological and physical effects that can be unpredictable at times. It can relieve pain, control nausea and increase appetite. Marijuana typically gives a high, or feeling of well being, which is why it abused. But marijuana can also cause acute psychosis, or a temporary break with reality. Marijuana-induced psychosis happens more often in new users or in people prone to mental illness.

Marijuana can cause short-term memory and learning problems, dry mouth, impaired motor skills and red eyes. Within minutes after smoking marijuana, the drug increases the user's heart rate. Heart rates can double in some cases, which is a risk for people with certain heart conditions. Some people may feel relaxed after using marijuana; others may develop anxiety and paranoia. A person's reaction to the drug partly depends on the individual, the strength of the marijuana used and whether the person ate or smoked the drug.


A debate continues on marijuana's benefits as a medicine. During a 2004 congressional testimony, a doctor speaking on behalf of the FDA said marijuana as a “botanical product” is difficult to test for efficacy and safety because the proportions of active chemicals can range greatly from plant to plant. This, he said, can also cause problems for patients trying to use marijuana.  But he added that the FDA “will be receptive to sound, scientifically based research into the medicinal uses of botanical marijuana and other cannabinoids.”

Scientists have identified more than 400 chemicals in marijuana. At least 66 compounds, called cannabinoids, are unique to marijuana. THC, or tetrahydrocannabinol, is the most well-known cannabinoid. Research has shown that THC binds to nerve cells in the body that have cannabinoid receptors. When THC binds to a nerve cell, it changes the activity of that nerve cell. 

THC has been known to decrease pressure within the eyes, raise anxiety and cause paranoia. However other cannabinoids produce different effects and may counteract THC. Cannabidiol, for example, reduces anxiety and paranoia. The proportion of THC to other cannabinoids varies by the cultivated strain, so the psychological effects of using marijuana can depend on the particular sample at hand.


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