Some psychoactive drugs facilitate the activity of a neurotransmitter by preventing the reuptake of the neurotransmitter into the presynaptic axon terminal. In doing so, the neurotransmitter is present in the synapse for a longer period of time having its effect on the postsynaptic neuron.

Cocaine and amphetamines are examples of drugs that act by this agonistic mechanism.  Their ability to block the reuptake of dopamine is thought to be responsible for their euphoric effects on behavior. The most commonly prescribed antidepressant medication today, Prozac, is a selective serotonin repuptake inhibitor (SSRI) which means that Prozac blocks the reuptake of serotoin in the brain.

In the scene below, the red squares 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