At socially relevant doses, Δ-9-THC raised plasma cortisol levels in a dose-dependent manner but frequent users showed blunted increases relative to healthy controls. 

right. so, this is proof of two things:

1) moderate thc use increases cortisol levels
2) you can actually smoke yourself stupid.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2863108/