Thanks, guys, for the replies. It seems this is a problem that affects several of us. I'm concerned about it because I found the following info about Mestinon: Notify your doctor if this medication appears to be losing its effect. In some cases, people become insensitive to the medication and it must be stopped for a brief period. Talk to your doctor about this.
I don't remember where I found that, and forgot to copy the web site, but I found similar info in a handbook at www.mgauk.org.uk which says: Since Mestinon’s effects last only a few hours, it is more important to take it often than to worry about the exact dose, which varies a lot between patients and from time to time in the same one. Generally it helps to keep the dose between a half and one and a half of the 60 mg Mestinon tablets (i.e. 30-90 mg) every three or four waking hours. Always keep on the low side to avoid both side effects on the one hand and tolerance on the other (when it becomes less effective with time).
The thought of having to go off my Mestinon for a brief period of time in order to restore its effectiveness kinda scares me. But better that than to develop increasing tolerance to it and have to keep taking ever increasing dosages.
Lizzie, I'd appreciate your posting your doctor's reply, if you are able to ask him (her?) about this. As I've mentioned in several other posts, I'm just under the care of my GP, not a neuro.
Hugs,