My drug stash

What's the best way to store prescription drugs to prolong their life?  I'm

specifically interested in storing Darvocet and Percocet.  (OK, really the

generic versions of both.)

I got prescriptions for them when I had kidney stones a couple months ago 
and took only a couple tablets.  I'm a bit paranoid now about waking up in

the middle of the night with another attack of kidney stones and would
like 
to have the meds around just in case.

Stored under best conditions, how long will they be effective?

Anny