First of all, I am not advocating the use of illegal drugs. However, marijuna or more specifically tetrahydrocannibanol (THC) use is more basic to our physiology than most would have guessed. THC binds to and stimulates specific receptors in areas of the brain associated with mood, memory, pain, and appetite. This explains marijuna's medicinal application and recreational use.
'Runner's High' is sometimes described as a similar, addicting euphoric state some people experience with exercise. For many years it was thought to be do to increased levels of endorphins. However, this explanation failed to hold water because endorphins do not cross the blood-brain barrier and therefore can not affect areas of the brain associated with mood.
The discovery of cannabinol receptors in the brain led to the question of why? Was there some similar molecule that the body made that also binds to these receptors? Sure enough, endocannaboids (cannaboid-like molecules produced in the body) were discovered. Two, similarly-structured lipid molecules (which do pass through the blood-brain barrier) were found.
Even more interesting, is that exercise raises endocannaboid levels. The 'runner's high' now has a biologically plausible mechanism. Elevated endocannabanoids activate cannabinoid receptors in the area of the brain associated with pain sensory and feeling good.
I think this powerful neuromodulation is what regular exercisers have discovered and seek to maintain. They have withdrawals when they don't get a chance to exercise. I also promote the "feeling great" sensation as one of the greatest benefits from exercise training.
Now that the mechanism behind the runner's high has been explained we can add one more drug to the 'exercise pill'. Next, just need to figure out how to modulate that exercise fat-loss mechanism. I am sure someone would be intersted in that.