Many of the drugs of abuse share the tendency to increase levels of which neurotransmitter in the brain?

Drugs of abuse such as methamphetamine and morphine increase the levels of dopamine in the central nervous system. Dopamine has a variety of functions but functions mainly in motivation and reward mechanism. People doing drugs of abuse create a pleasurable sensation in which there is a dopamine surge every time they use drugs. In the absence of drugs, the body "looks" for the pleasure thereby causing the person to be drug-dependent and addicted.