Hey smilly, sorry, I think I've been studying/examming too much!! -_- >_< .....
What I mean is that the amount (or quality) of receptors for the drug (phentob. in this case) is less than most people. So the effect you get from x-amount of drug is less and hence it'll take you more to achieve the same amount of effect (as others might). This occurs with many drugs - more so some than others.
Having said that, please remember that you can always take more, but once taken you can't "untake" it. Meaning be safe, start off with small quantities and titrate (work your way) up. One more hint, barbiturates (especially orally) are known to take quite a while for the effects to start. So you might take some, think it's not working and take more. Just watch out for that.
One last thing,
DON'T drink whilst on any barbiturates! People drink whilst on on benzos - which they shouldn't really by all accounts but at least they're a lot more forgiving than barbs! - but it's a lot more easier to OD on polydrug use of the combo alcohol/barbs!
Oh, of course in the end they could just be bunk, there's no way of me telling from here. lol
Anyway, be safe brother!
On the prescription in Aus side of things, I can tell you that it
is prescribed, just
quite rarely. It's even on the
PBS listing.