Chris,
Probanthine/Propantheline are the same thing, one of them being a trading name (I can't remember which). I have posted quite a lot on this medication in threads below and take it occasionally. I probably have taken no more than 40 tablets over the last 20 months when I had them prescribed by my doctor.
They generally do work for me but are short lasting, perhaps 3-4 hours or so. I take them on an empty stomach or they don't work. I have never taken them on a daily basis because I think they will become less effective and others on here have said similar. That said, my prescription is for a daily dose but I have ignored it..
However, when I want to be dry, I take the tablet about 30-45 minutes beforehand on an empty stomach as said. My prescription states that I can take up to 2 at a time and up to 3 times a day, but I only use them before a public sweaty event that I know is coming. It has worked wonders on me when taken before going out for an indian meal with friends when I would normally sweat profusely from the head and neck or when travelling on the tube. It has also worked when out walking when taken this way. But, I too have had the odd occasion when it hasn't worked, but it has been 95% success so far when taken at limited times.
It does give a dry mouth but that is not an issue, just drink water. The only odd side effect I have had is a mild tingling and slight perspiration on the front of my legs, but again only very mild. I actually use this sensation to know that it's working. I don't think I have taken enough or over a long term to know of any longer lasting effects, but my doctor has not warned me of anything to be concerned about.
I have just got 50 tablets from my doctor at a cost of £6 which is the UK prescription charge.
I have just found this site by doing a search that sells them over the internet
http://www.cprx.com/productlisting.asp?page=8&ch=P
but I have to say I know nothing about them or how reputable they are to deal with so that would need to be checked. Also I have no medical knowledge of any type to know if these would be ok for you, so perhaps ask a doctor before trying.
Good luck,
Bill