By the look of a recent paper in Nature Neuropsychopharmacology, the problems of psychosis caused (in the small number of people that are susceptible) by smoking too much cannabis could possibly be cured by…. smoking cannabis! It’s the strain that makes the difference, suggesting that a "government approved labelling standard" and a different legal status for each strain might be worthwhile – or even that the government should give away seeds from good strains!
There are two major cannabinoids in Cannabis sativa, Δ-9-Tetrahydrocannabinol (THC) and Cannabidiol (CBD), both of which are psychoactive (especially for medicinal purposes like painkilling), but with THC being the most intoxicating.
It seems that for those few that can be pushed towards or into psychosis by pot smoking, it’s the THC that causes the problems, while CBD not only doesn’t cause the problem, but protects against at least some the dangers of THC.
This might well tie in with the newer strains of cannabis, "skunk", that have much higher levels of THC and lower levels of CBD, probably by a skewing of the metabolic pathways away from CBD in favor of THC rather than simply increasing the amount of THC produced by upping activity of the pathways leading to both.