Before taking methylene blue, and if you have genetic origins from high risk areas (Mediterranean, African, SE Asia), make sure you know that you don’t have G6PD. As with all antimalarials, G6PD may result in haemolysis. Of course it’s also on every blue dessert etc. , but don’t take your previous exposure as sign of immunity. Haemolytic episodes are possible but not given and as such you can consume the substance with minor signs for years and still end up with an episode.