It's a myth. It only increases aggression if you're a hot head to begin with. If you're easy going and mellow, you'll stay easy going and mellow, with more focus/intensity in the weight room. All the big boys I know are some of the nicest people. The only guy I know who has "increased aggression" is the same guy who stacks orals only and goes to the bar looking to prove how tough he is every weekend...