I think the increase in tolerance requires a healthy liver.
Your brother's is the third case I have read that is unable to ramp up the dosage.
All had a compromised liver function.
The good news is, the active ingredients stay in the body at a higher level, for a longer time.
That's why he feels so stoned. Kind of a "cheap drunk" thing.
It should be as effective as a larger dosage is in a person with normal liver function.

At least that's my take on it.
I am NOT a doctor.

Aloha,
Weezard