Fact: There is no convincing scientific evidence that marijuana causes psychological damage or mental illness in either teenagers or adults. Some marijuana users experience psychological distress following marijuana ingestion, which may include feelings of panic, anxiety, and paranoia. Such experiences can be frightening, but the effects are temporary. With very large doses, marijuana can cause temporary toxic psychosis. This occurs rarely, and almost always when marijuana is eaten rather than smoked. Marijuana does not cause profound changes in people’s behavior.