Yeah, loperamide is OTC everywhere as far as I know.
(Brand name 'Imodium').
As for potentiating - I don't think it would work particularly well.
It
would cause a potentially dramatic increase in constipation if added to bupe or other opioids - but in and of itself, it is only "active" in a very peripheral sense (at least in my experience - some people report getting some opiate effects from massive doses, but if you track down the loperamide 'big and dandy' thread, there is plenty of evidence there to suggest that such large dosing is very dangerous and has killed several Bluelighters).
Yes, loperamide offers many people a fairly straightforward way to manage withdrawals - particularly the physical side; the GI discomfort and other physical responses to withdrawal.
Some users report an easing of the mental symptoms of opiate withdrawal, but one of the problems with this is that in sufficiently high doses, you may well get WD symptom relief, but you may also find that you're swapping one habit for another - and I understand that withdrawing from loperamide is pretty fucking nasty.
So...lope is pretty useful when used appropriately - for detox and the later stages of acute withdrawal.
Or for times that you get caught short, and need to work (for example) - but I wouldn't recommend incorporating it into an addict's regular drug regimen - instead, save it for when you need it to get by.
There is a wealth of information
in this thread - but I take some of it with a grain of salt.
Dosing hundreds of milligrams might stave off withdrawals from your drug of choice...but it may also have far more serious consequences than conventional opiates/opioids.
I only ever took lope "as directed" for the help it offered to get through life whilst dealing with withdrawal.
This is after a serious taper - which is what I would advise anyone do.
Abusing loperamide is fucking dangerous - while it is a handy tool, it is by no means a miracle drug or a "get out of jail free card".
Think of it as another tool that can be used to cope with the more uncomfortable parts of opiate withdrawal.