I was taking mestinon five times a day. At thanksgiving time I was in the hospital for ptosis. They thought maybe I was having atypical migraines. They gave me 3 iv piggybacks of magnesium and then sent me home with a magnesium prescription. I have been feeling weak ever since I was in the hospital. My doctor increased my mestinon to 6x/day but I was still feeling week. Then last week I was having diarrhea so I decided to skip my magnesium for a couple of days to see if that helped. All of a sudden I had all of my strength back! I am positive it was the magnesium, but when I called my doctor's office they said they didn't think it was related. Has anyone else had trouble with magnesium?

Magnesium is one of the things to avoid if you have a myasthenia. I got really weak just from taking a lot of tums because I didn't think about them containing magnesium as well as calcium.
Just google magnesium and myasthenia gravis and you will see that it is in the list if drugs to avoid. Do you have an mg specialist. Your doctor should know this.

I do have a specialist but when I called I talked to an intern. Maybe that was the problem. He told me to talk to my headache neurologist. The reply I got from her secretary was that it should not interfere with any of my meds but if I wanted to stop taking it I could. So I am really annoyed that I talked to two neurologists and neither one of them seemed to think magnesium should cause problems. Well I am telling you all that it does. I talked to a nephrologist friend of mine and he said absolutely magnesium could cause problems because it works at the same site as mestinon.

I think therapeutic dosing as in high doses for a "treatment" would be not good for MGers. High dose treatment is used as you describe, also IV for migraine, and for hypertension eclampsia of pregnancy. In fact I believe the eclampsia paper is easily retrievable on PubMed.

However MGers should have the daily RDA of magnesium for general health. Without you can develop heart arrhythmias, and
many other problems. Magnesium is used in many biochemical maintenance functions in the body.

In other words, some to maintain yourself --ideally from food which is slower onset than supplements. And not massive therapeutic doses. It is a fine line to walk and maintain.

when I became sick initially someone told me to take magnesium that it would "help" my muscles! ha! I was soooo weak, it was awful! I will never touch the stuff again!

Me neither! I am glad to see I am not the only one