I don't take mestinon, but have a friend who's had MG for almost 30 years, and she was told that using high dose for extended periods will destroy some of the acetylcholine receptors. Over time, that could cause more muscle damage and weakness.

In my opinion, if you're needing that much mestinon, an additional med might need to be considered, as that dosage is not indicative of well controlled symptoms. In addition, when you get dosages that high, the risk of overdosing does increase.

Hope this helps (and doesn't scare.)