Smoking marijuana causes some changes in the brain that are like those caused by cocaine, heroin, and alcohol. Some researchers believe that these changes may put a person more at risk of becoming addicted to other drugs, such as cocaine or heroin.

Marijuana’s effects on the user depend on its strength or potency, which is related to the amount of THC it contains. The THC content of marijuana has been increasing since the 1970s.

Generally, traces of THC found in marijuana can be detected by standard urine testing methods several days after a smoking session. However, in chronic heavy users, traces can sometimes be detected for weeks after they have stopped using marijuana.

Long-term marijuana use can lead to addiction in some people. That is, they cannot control their urges to seek out and use marijuana, even though it negatively affects their family relationships, school performance, and recreational activities.