Drugs can stimulate or block dopamine receptors. Drugs can also act directly or indirectly on those receptors. What's more, neurons can become sensitized or desensitized to dopamine. Enzymes and drugs affect dopamine levels. Other neurotransmitters can be compared to dopamine.
Drugs interfere with neurotransmitters.
Drugs can affect almost every step in the communication between neurons. For example, drugs may bind to receptors in place of neurotransmitters, block neurotransmitters from entering or leaving neurons, or stop the chemical reactions that create neurotransmitters.