Last time I looked at the Metamucil-capsules package at the store, I believe it said the daily dosage was about 10. (5 twice a day). I believe it's just the drink-mix powder but in capsule form, so going over the limit a bit is harmless. What he should worry about though is water intake. Taking that much fiber requires you up your water intake by a ton.
Personally, Metamucil gave me horrible stomach cramps and minor gas - and the resulting poop looked as poopy_dipes said - like brown spongy brains. I stopped using it after a few retries. Too painful and disgusting.