Originally Posted by KarlGauss
I agree with you. That is the literal definition of an agonist.
Still, in casual parlance we often use the term 'agonist' to denote an agent which potentiates or stimulates the receptor regardless of its mode of action. An example might be any of the acetylcholinesterase inhibitors (i.e. donezepil et al) which while not directly stimulating the acetylcholine receptor, have a net effect to augment cholinergic transmission.
I realize I should have defined my understanding of agonist and antagonist, which is the same as Shagnasty
said. An agonist would be something that binds to, and activates, the particular receptor it is an agonist for. And an antagonist would be something that binds to the receptor but does not activate it, thus preventing whatever is supposed
to bind to the receptor (and activate it) from doing its job.
So then, Prozac is not an agonist in the technical sense (and, in fact, according to Shagnasty
's cite, it may actually be an antagonist) but people often call something an agonist when it has the effect of activating its particular receptor, even if it does so indirectly (by merely increasing synaptic concentration of the endogenous chemical that binds to and activates the receptor, say) like Prozac? I wondered if that might be the case, but it seems pretty imprecise...