Can you take six xanax in three hours?

You shouldn't ever take larger than the prescribed dosage.

Largest produced individual Xanax, alprazolam, pill 2mg (that I know of)

Smallest produced individual Xanax, alprazolam, pill 0.25mg (that I know of)

2mg x 6 = 12mg

0.25 x 6 = 1.5mg

I suggest either following your doctor's suggestion, or realize for yourself that above 2mg the chemical will be dangerous.

If you have to ask on Yahoo answers whether you can take it or not, the answer is most likely you cannot or should not

For Drug information consult a doctor first. If unable to contact a doctor, a second source could be www.erowid.org