I have never taken any prescribed drugs for my Myotonia Congenita, but was seriously considering Mexiletine. I then discovered a book "Deadly Medicine Why Tens of Thousands of Heart Patients Died in America's Worst Drug Disaster". I found the book a fascinating read, and I suggest you think about reading it. I have no doubt that Mexiletine works but that there are significant dangers, particularly when used on a long term basis. I decided not to take it.

My sister who also had MC died after taking Procainamide for over 20 years, and I am convinced that there was a very strong connection. Maybe she thought the risk was worthwhile. I did not and told her why 36 years ago

Here is a summary of the book.

Deadly Medicine is a human story about the brilliant and driven doctors who worked on Tambocor and similar heart drugs-at pharmaceutical companies, within the FDA, and at university medical research centers. It provides a vivid and disturbing account of the system by which drugs are discovered, tested, and marketed to doctors. Through the tragic story of how tens of thousands of patients died prematurely from one class of heart drugs, Deadly Medicine also exposes major flaws in this system.

Chapter 16 (pp. 163-176) first describes the typical promotional practices of drug companies: gift giving, sales representatives, paying doctors large sums to participate in studies of dubious value and buying prescribing data of physicians details. The chapter then goes on to describe how 3M and Bristol Myers, makers of the heart drugs Tambocor and Mexetil, employed leading American cardiologists to lecture about their products at symposia. It also presents critical evaluations of journal advertisements for Tambocor and the reaction of the Food and Drug Administration to these ads.