He can briefly hide the influence and pay attention but easily loses focus. Coming down from a high may be the worst for motor skills. Occasionally get a triggered unexpected after-high. Reckless driving, failure to yield, failure to stop. STOP for two months and see if symptoms go away.
First stage is exposure.
Develops a preoccupied with chemical dependence life style. Uses first in the AM, last at night, using it just to function. The percentage of use of cocaine is directly related to the frequency of use of pot. In stage four with increased tolerance the addict uses more of the higher grade THC, starts mixing drugs, seeks out more heavy using friends. See social and school deterioration, dropping off team, dropping hobbies.