First I will say that I have not tried the zenmed myself, but everything I have ever read about those kind of supplements is that the reason you only take them for a few months is because your body builds up a resistance. The same can happen with taking Antibiotics . Once you stop the pills, you take a few months for your body to flush itself out. But then you have to start taking the pills again. Your son would have to do this on-and-off routine for the rest of the time he has acne. Taking the pills will only help control the Acne - it can't rewire his brain to correct the hormone imbalances that cause Acne in the first place.
That said, whether he takes the zenmed capsules or some other pill, or uses a topical cream, or whatever, it's something that will have to continue as long as he has Acne anyway. I would say the zenmed is worth a shot. If it works, rad! If not, then he will try something else, like we all do:)