The brain is made up of nerve cells that send messages to each other by releasing chemicals called neurotransmitters. Most depressants affect the brain by increasing the activity of the neurotransmitter gamma-aminobutyric acid (GABA). The increased GABA activity in turn slows down brain activity. This causes a relaxing effect that is helpful to people with anxiety or sleep problems. Too much GABA activity, though, can be harmful.
Learn more about how the brain works and what happens when a person misuses drugs.