All drugs affect the brain. That's why they can make you feel high, low, fast, or slow, or make you see things that aren't there.
Some drugs can hurt your brain and affect how you act and how your body feels. These problems might last just a little while, or they may last for the rest of your life.
Some drugs can make your moods change quickly. You might get sad, angry, or scared for no good reason. You might overreact to little problems. Drugs can make you act crazy. You might see or hear things that aren't there. You might get violent or think that someone wants to hurt you.
Some drugs can make it hard to pay attention, remember things, or even think clearly. That's why people often make bad decisions when they're on drugs.
Drug use can hurt your ability to enjoy things. When you're addicted, things that used to make you feel good—like seeing friends or watching a movie—no longer make you happy. Usually, you can start enjoying things again once you stop using drugs, but it may take time.