Question about agonists in general

[Aiken]

I just mentioned getting some samples of Rozerem, a melatonin agonist, in my opioid buildup thread. I have a more general question about agonists, though, and I figure this ought to be in its own thread.

Am I right that an agonist essentially amplifies the effect of whatever it's an agonist of? So, in this case, the melatonin agonist would cause the melatonin already in my system to cause a stronger reaction?

I ask because I have a theory that my body doesn't actually produce any melatonin, at all, anymore. Without supplement, I practically have no daily rhythms. My blood pressure, my temperature, and so on, tend to be a flat line all day. Staying up all night, unmedicated, physically exhausts me, but doesn't actually make me very sleepy. Taking nightly melatonin is the only thing that seems to create an actual cycle. I get kind of cold, relaxed, and sleepy a couple of hours after taking it. (Which is, of course, pretty useless in the face of RLS, but that's what other meds are for.) I wonder if this melatonin agonist will be completely useless without any melatonin. I've seen other people say it did nothing and I wonder if that was their problem.

[Neco]

Agonists don't really boost the effect of a molecule in your body, what it does is binds to the same type of receptor cell. For example, opiates bind to opiod receptors an effectively saturate the system (causing your body to grow more connections and require more opiates, starting a cycle of dependance, more or less).

So while I'm sure there are drugs that can encourage your body into making melatonin, chances are you're taking a melatonin supplement that is really just replacing your natural melatonin at the receptor site.

As far as I know this explanation is factually correct, but I could be slightly wrong as well.