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SourceNational Institute on Drug Abuse Back To the Table of Contents ForumsHealth, Safety, Nutrition and KidsRelated ArticlesGrowing Up Drug Free: A Parent's Guide To Prevention
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 Q: What happens after a person smokes marijuana?A: Within a few minutes of inhaling marijuana smoke, the user will likely feel, along with intoxication, a dry mouth, rapid heartbeat, some loss of coordination and poor sense of balance, and decreased reaction time. Blood vessels in the eye expand, so the user's eyes look red.For some people, marijuana raises blood pressure slightly and can double the normal heart rate. This effect can be greater when other drugs are mixed with the marijuana; but users do not always know when that happens. As the immediate effects fade, usually after 2 to 3 hours, the user may become sleepy.
Q: How long does marijuana stay in the user's body?A: THC in marijuana is strongly absorbed by fatty tissues in various organs. Generally, traces (metabolites) of THC can be detected by standard urine testing methods several days after a smoking session. However, in heavy chronic users, traces can sometimes be detected for weeks after they have stopped using marijuana.
Q: Can a user have a bad reaction?A: Yes. Some users, especially someone new to the drug or in a strange setting, may suffer acute anxiety and have paranoid thoughts. This is more likely to happen with high doses of THC. These scary feelings will fade as the drug's effects wear off.In rare cases, a user who has taken a very high dose of the drug can have severe psychotic symptoms and need emergency medical treatment. Other kinds of bad reactions can occur when marijuana is mixed with other drugs, such as PCP or cocaine.
Q: How is marijuana harmful?A: Marijuana can be harmful in a number of ways, through both immediate effects and damage to health over time.Marijuana hinders the user's short-term memory (memory for recent events), and he or she may have trouble handling complex tasks. With the use of more potent varieties of marijuana, even simple tasks can be difficult. Because of the drug's effects on perceptions and reaction time, users could be involved in auto crashes. Drug users also may become involved in risky sex. There is a strong link between drug use and unsafe sex and the spread of HIV, the virus that causes AIDS. Under the influence of marijuana, students may find it hard to study and learn. Young athletes could find their performance is off; both timing and coordination are affected by THC. Some of the more long-range effects of marijuana use are described later in this document.
Q: How does marijuana affect driving?A: Marijuana has adverse effects on many of the skills needed for driving a car. These effects may include difficulty in judging distances and delayed reactions to sights and sounds that drivers need to notice.There are data showing that marijuana plays a role in crashes. When users combine marijuana with alcohol, as they often do, the hazards of driving can be more severe than with either drug alone. A study of patients in a shock-trauma unit who had been in traffic accidents revealed that 15 percent of those who had been driving a car or motorcycle had been smoking marijuana, and another 17 percent had both THC and alcohol in their blood. In Memphis, Tennessee, researchers found that, of 150 reckless drivers who were tested for drugs at the arrest scene, 33 percent showed signs of marijuana use, and 12 percent tested positive for both marijuana and cocaine.
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