Some psychoactive drugs act as antagonists by blocking a neurotransmitter's receptor sites on postsynaptic neurons.

Traditional antipsychotic medications (e.g., Thorazine, Haldol) work in this manner. These antipsychotic medications block dopamine receptors on the postsynaptic neuron which prevents dopamine's ability to act on those postsynaptic receptors. Their ability to block dopamine postsynaptic receptors is thought to be responsible for their ability to reduce the core symptoms of schizophrenia (i.e., thought disorder, delusions, hallucinations) .

In the scene below, the red circles represent the molecules of the drug.

You may view this agonist mechanism by clicking on the "Play" button in the scene below. To view the animation again, you must first click on the "Rewind" button