It's definitely difficult to say no to your best friend, especially if you want to fit in. If your best friend or a peer offers you drugs, try to change the subject or find something else for you guys to do. It's a much better alternative to doing drugs.
Even if the drugs are a prescription and are used for physical or mental health reasons, it's still important to be careful about how much you are taking. Overdoses can lead to serious probelms.
Teens want to feel grown up, and doing drugs makes them feel that way.
Being an adult isn't all fun and games, especially if you do drugs. Instead of doing drugs to feel grown up, try acting more mature by taking up more responibilities.