Almost all of the drugs that change the way the brain works do so by affecting chemical neurotransmission. Some of these drugs, mimic the effect of a neurotransmitter, prevent messages from getting through, interfere with the molecules responsible for transporting neurotransmitters back into the neurons that released them, or, cause neurotransmitters to be released in greater amounts than normal. Drugs that affect the feelings, perceptions, or behavior of the user have psychoactive (mind-altering) properties.