I will say that Rooth has covered everything quite well.
Yes, symptoms of something just means that you have symptoms of something.
The only thing that drugs are intended to do is quiet the symptoms, not get to the cause.
A note on the asthma.
In Hulda Clark s book she describes the parasites causing asthma. (see, there's the cause) (look under respiratory illness)
He could very well benefit from some good parasite cleansing.
As for doing the cleanse while taking prescribed drugs. That would be up to his judgment.
Drugs are toxic to the body. So you have toxic stuff being cleaned out of the body by The Master Cleanse and you have similar stuff going back in at the same time.
I once attended a health lecture where it was said that "All medications are drugs and all drugs are poison to the body".