I never looked. Seriously, methylene blue has been used as a drug for more than 100 years. IIRC, it’s the first drug the FDA approved. I think the body clears i

I never looked. Seriously, methylene blue has been used as a drug for more than 100 years. IIRC, it’s the first drug the FDA approved. I think the body clears it reasonably quickly and I would not expect it to permanently stain your insides.