Most recreational drugs (excluding the harder ones and depressants i guess) probably contribute more to neurogenesis than they do to neurodegeneration. The antidepressant effects achieved by chronic use of some drugs can be attributed to neurogenesis in the hippocampus, which is the mechanism theorized to underly how SSRIs change the brain. Learning new information, even without the influence of any psychoactive drugs, causes DNA breakage in brain cells which is eventually patched up/pruned for a more efficient brain. Getting your body to undergo the neural adaptations in leisure that would normally only occur in rare/dangerous/spiritual experiences enhances the amount/type of data the brain can handle. In that sense I agree with Terrance McKenna's stoned ape theory. When you take all the serotonin and put it somewhere else after eating a handful of magic mushrooms, it's like subjecting everything to either a new type of skill or to natural selection. Hell, I'd even bet the psychedelic experiences that starter fluid can generate probably looks interesting in upregulation/downregulation on a brain scan, and may contribute to intelligence. More effort needs to be put into examining the changes in cells of neural tissues after acute/chronic administration of chemical XYZ
