A recent (2005), major clinical study found that chronic and heavy cannabis use reduced anxiety and depression due to significant brain cell regeneration. The study conducted in Canada and funded by the Canadian Institutes of Health Research (CIHR) went out to prove that cannabis can create neurogenesis (brain cell regeneration).
Heavy, chronic use was the key!
The most impactful factor on this study was the amount of cannabis concentrate used on the rats. The adult rats were administered a very high dose, twice daily. The result was ground breaking as doctors sited a significant growth of new brain cells in the adult rats. They concluded that due to the effect of these high doses of cannabinoids, the rats were much more active and willing to eat.
Earlier studies used low doses of cannabinoids.
Earlier studies similar to this study came up empty because they were using lower doses of cannabinoid and administering them less frequently. These studies showed little to no benefit for the rats and neurogenesis. So the more cannabis you take the better off you will be!
Vaporizing dry herb is the most therapeutic method.
When it comes to the most healthy and overall "best feeling method" of human cannabis consumption, dry herb vaping is by far the best. Studies comparing vaping to smoking weed prove that you will get more of the essential cannabinoids like THC and CBD without harmful toxins. Smoking's very high temperatures will also destroy and burn off up to 95% of these beneficial cannabinoids. So feel free to vape your dry herb until your heart is content because the more cannabinoids you ingest, the healthier and younger your brain will be!
Here is the link to the study again: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1253627/