It's a bit more complex than that....beyond just agonists and antagonists, with the way all of the cannabinoids end up interacting with each other, and the other trickle down effects on other systems, etc. I have a rather basic understanding of pharmacology, and a decent knowledge of cannabis, so I'll attempt to explain what I can.
I believe you're correct that THC is the only cannabinoid in cannabis that is actually an agonist, being a partial agonist at CB1 & CB2.
The other cannabinoids that you listed do have some antagonistic properties on the cannabinoid receptors...But they mostly have low affinity for CB1 & CB2 in comparison to THC (this is all very generally speaking)...and I'd say this is part of the answer to what you're asking. Affinity is the drugs ability to bind to a receptor. Depending on the affinity a drug has for a receptor, the duration & strength of antagonist or agonist activity will vary. So CBD, as an example, isn't all that "sticky" to CB1 & CB2 (low affinity), where as THC is stickier to these receptors (higher affinity).
So these other cannabinoids don't cause much "blocking" of THC's effects via antagonism, because the THC has a higher affinity for the receptors.
Then there's all sorts of other actions that some cannabinoids have...Cannabidiol(CBD), for example....CBD indirectly stimulates endogenous cannabinoid (cannabinoids naturally produced in the body) signaling by suppressing the enzyme "fatty acid amide hydroxylase" (FAAH). It is this enzyme which breaks down anandamide. Anandamide is an endogenous cannabinoid naturally produced & found in the body, which binds to cannabinoid receptors, favoring the CB1 receptor.
Because that enzyme, FAAH, is suppressed by CBD, less FAAH means more anandamide remains present in the body for a longer duration. More anandamide means greater CB1 activation .
....and that's just one aspect of CBD, imagine all the other complex things going on with the rest of the cannabinoids.
And there's also well over 100 different terpenes in cannabis that have a quite an influence on the collective effects of the cannabinoids. These terepenes are what give cannabis its aroma & flavor. The terepenes are also the pre-cursors of cannabinoids, they are the building blocks of the cannabinoids. By themselves they're not really all that "psychoactive", but they do have an influence on the effects of cannabis. Picking one for an example, the terepene myrcene makes the blood brain barrier a bit more permeable for cannabinoids and allows them to cross the barrier more easily, generally potentiating and prolonging the effects of THC and the collective effects of the herb in general.
Each strain has a unique profile of terepenes....I believe these terepenes are the key players in cannabis having a broad spectrum of effects & medicinal uses, differing from strain to strain, more so than the cannabinoids themselves. Sure the cannabinoids are the primary psychoactive substances in the herb, but the terepenes are like the "seasoning" on top, that really bring certain aspects out and add a "Zest" to the effects . Influencing things like, how quickly the effects come on, how long the effects last, how clear headed the effects are, how analgesic the effects are, etc etc. So it's each strains unique profile of terepenes, on top of the unique profile of cannabinoids, that gives us all these various effects.
Shit gets all sorts of complex when it comes to medicinal plants. All medicinal plants tend to have a wide spectrum of chemicals that interact with each other so very elegantly, potentiating and balancing each other out, to provide us with the beautiful effects that they do.
-OM

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Edited by openmind (10/24/13 08:17 PM)
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