Agonists and Antagonists

There are many ways that a drug can alter how a synapse functions. However, we can group all the effects into whether the drug increases the effect of the neurotransmitter at the synapse or decreases it. If the drug increases the effect of the neurotransmitter it is called an agonist. If it decreases the effect of the neurotransmitter it is called an antagonist. So, if a neurotransmitter is inhibitory, an agonist will increase the inhibitory effect of the neurotransmitter, whereas an antagonist will decrease the inhibitory effect. If the neurotransmitter is excitatory, an agonist will increase the excitatory effect, and an antagonist will decrease the excitatory effect. (Return to To Fire or Not to Fire, for a quick review of inhibition/excitation.)

The next sections will describe some of the different ways that a drug can be either an agonist or an antagonist and then will provide examples of where some familiar drugs fit into the picture.


Agonist drugs that:
Mimic Neurotransmitters
Stop Removal of Neurotransmitters from the Synapse
Increase Production of Neurotransmitters

Antagonist drugs that:
Block the Receptor Sites
Speed Removal of Neurotransmitters from the Synapse
Decrease Production of Neurotransmitters