ABSTRACT
Psychoactive drugs alter activity at nervous system synapses. A synapse is the place where messages pass from one neuron to another. Chemicals known as neurotransmitters pass the messages from neuron to neuron. Drugs can impact on the activity of neurotransmitters, either directly or indirectly. An agonist increases the action of a given neurotransmitter whereas an antagonist decreases or blocks it.
