Can I take Mensil or another medication for "longer sex" with myasthenia gravis?

Myasthemia is not an absolute contraindication to the use of drugs with sildenafil (Mensil). There should be no harmful interactions between the listed drugs or the effects of drugs. Nevertheless, I encourage you to inform the attending physician about the introduction of a new drug into therapy. Perhaps your doctor will make other recommendations about how to use them. I also encourage you to read the article: https://www.gdziepolek.pl/artykuly/leki-na-potencje https://www.gdziepolek.pl/substancje/sildenafil