I lucked out today. I have been using Methylene Blue for a long time. I ordered the powder from Amazon. When I went to order more, the Amazon page I had ordered was gone, but I found a different powdered version that said it was USP (pharmacy grade).
I have had questions about the new brand since I started using it about 3 weeks ago. It does not make my tongue nearly as blue. I can easily wash it off my skin. The last few weeks my tongue has been really sore with canker sores. Yuck.
I'm not saying the new brand is what is hurting my mouth, but I am saying this new stuff is different and not impressive as far as staining things blue. I bought 3 grams for $60 ($20 per gram) and I am done with using it (maybe I will try to dye something with the 2.5 grams I have left).
The good news: I was wondering what a good brand of Methylene Blue would be and I found this video today: Methylene Blue - updated youtu.be/p97zv5SFls4
And this guy highly recommends CZTL Methylene Blue: cztl.bz/?ref=Lwr85
It turns out CZTL was the first brand I bought a year ago, it was great and I am ordering more.
CZTL costs $30 a gram at Amazon amazon.com/USP-Grade-Methyl... and I just ordered 1 gram overnight.
CZTL costs $70 for 5 grams at the CZTL site, so I will also go ahead and order 5 grams there (I don't know how long it will take to get here). cztl.bz/collections/feature...
For legal reasons, I am not going to mention the name of the other MB powder I bought at Amazon. I will just say I there are only 2 brands of powder MB at Amazon that I can see.