Legal for adults doesn't mean safe for teens.
Your brain is still a work in progress! Youth, teens, and young adults are at a special risk for harm from marijuana use because human brains continue developing until age 25.
Using cannabis before the age of 25 can lead to issues such as:
Protecting Your Mental Health
Marijuana use has been shown to increase the risk of mental health issues (like depression, anxiety, psychosis and schizophrenia) in teens and young adults. This risk is greater among young people who use cannabis more often and who use cannabis with a higher THC content.
Cannabis use can increase the risk of mental health issues including:

Health Risks

Because it comes from a plant, some people don't realize the risks of cannabis use. In reality, cannabis is a psychoactive (mind-altering) substance like many other drugs. Using cannabis can cause physical and mental issues, especially in developing teens. These issues can include:
If you use cannabis, tell your doctor. Some medications have harmful interactions with cannabis that can put your health at risk.