I wouldn't say any OTC "Benzo" like substance would be strong enough, I have never heard of any such thing existing.
Also, you can test your drugs with drug test reagents. Also if they're you friend, I doubt they would trick you???
As a fellow drug user, whose uses benzo's, I've never OD'ed on Xanny but I'm sure it's possible, probably 10m-20mgs with booze.
Not to sure.