s just taking hydrocodone, and not mixing with other drugs or alcohol, it would take alot to
overdose. Especially if he has a tolerance. I would say its more likely he would need to go to the hospital for APAP toxicity than hydrocodone overdose. APAP (tylenol) is mixed with the hydrocodone and is not good for the liver in high doses.
Just tell him not to go crazy and make sure he doesn't mix with alcohol or other drugs (besides weed), and he should remain alive.