It is neither an antagonist nor an agonist at any of the known receptors - also like the racetams.
The key to getting better receptor response is neither antagonists nor agonists - the brain up or downregulates to compensate - but restoring the speed, sensitivity and density of them. Piracetam for example causes an increase of up to 30% in the density of muscarinic acetylcholinergic receptors in addition to its other effects. This increase in receptor density only occurs when the existing density is substandard due to aging or damage and does not occur in young brains.
Aging and damage cause both a decrease in receptor numbers (density) and a decrease in per-receptor sensitivity along with other changes such as decreased available energy (ATP) and loss of membrane fluidity, however - the key thing to remember is that aging and damage do not alter the negative-loop feedback systems in proportion to the functionality losses in the systems that they regulate. That means that the brain will compensate to keep perceived signal strengths and speeds constant despite the losses that aging and damage cause. Thus, the brain's own lack of perception of its losses means that it will tend to sabotage efforts to compensate by external means if those means attempt to push or pull against its natural regulatory tendencies.
Those negative-feedback loops have their own ideas about what's optimal - or what was optimal, but they don't keep up with the times. They are the guardians - the ultimate gatekeepers that issue the rules.
A more sophisticated approach is to sabotage - bias - the regulatory sytems themselves instead of the systems they regulate, but that approach too has its problems. First it is simply more difficult, and second it still does not correct for the fundamentally decreased functionalities of the systems being regulated, so restoration of original ligand densities or increase above original values has by itself negative side-effects even if the agent(s) used to affect such a change themselves have no side-effects.
The only solution to this conundrum is to restore the original functionality, thus normalizing the ratio of function to negative-feedback inhibition that was preset by genetics at birth.
The racetams and some other molecules can by unknown and known means partially correct these deficiencies, making alteration of the regulatory systems unnecessary because those systems are already evolutionarily precalibrated for the correct values - assuming the organism was healthy to start with. If that is not the case then other treament(s) may be required or it may not be possible to achieve complete or even partial restoration.
Some individuals have by genetics at birth incorrect regulatory values and for them alternatives will be necessary. Paradoxically, for those with genetically inborn excessive activity, aging and damage itself can decrease that activity and thus the manic type may as they get older and/or more damaged lose or experience a decrease in such activity, leading them to believe that their brain health is improving when it is actually in decline. Paradoxically, racetams and other therapeutics that restore original functionality may bring back their old 'problems', but are still valuable therapeutics.
Restoring the youthful function may for these individuals mean the need to treat inherent problems that have become masked by the rust of aging/damage. They may mistake the positive therapeutic effects of functional restoration as negative if their original function was biased towards excessive stimulation and thus quit the agents instead of investigating further the cause. I have seen many cases on this forum and others of precisely this phenomenon, though it is not common.
For example, in my case I have a genetic bias toward light sleeping and awakening many times in the night. On first taking Piracetam I noticed it took longer to get to sleep at night, however I realized that I was sleeping better and this compensated for the decreased sleep hours. However, due to aging after starting Piracetam I no longer notice this effect but still notice far improved sleep quality and better total restoration by morning.
However, someone with one or more stronger genetic biases may not be able to reach a suitable balance without further corrective actions. Luckily I am not one of them.
Edited by Isochroma-Reborn, 02 April 2013 - 06:52 AM.