Marijuana & weightlifting in Bodybuilding/Strength Training Posted July 12, 2011 hey. This is a hypothetical question. Let's say I started serious weightlifting (olympic) a year ago and within a few months ago started smoking regularly. Once (yes only once) a day, after all other responsibilities are done and with a vaporizer (no tar and other negative stuff from combustion). Does the THC slow down your reaction/speed of the CNS? Can it negatively affect work capacity?