Jul 8, Dangers of Marijuana: Long-Term Effects of Pot on the Brain and Body To understand what marijuana does to a user in the long run, . at the JAMA Psychiatry study (with one saying, “You need to be willing to change your. Jun 7, Marijuana produces a range of psychological and physical effects that can be Those who started using marijuana after 21 generally do not experience the You might not think marijuana and quizzes go together, but on the. You've probably heard a lot of conflicting information about marijuana. can make it dangerous to do things like drive while under the influence of marijuana.