The active ingredient in Can-C is N-acetylcysteine (NAC).
I tried Can-C in 2014, but I gave up after 1 month because it made my yellow cataracts more yellow. I also tried Brite-Eyes III, but it didn't work either and the same thing happened. I wondered why these products made them more yellow/brown. I read somewhere on the Net that it's because NAC goes down the same metabolic pathway as the lens proteins, so you end up with the same colored end-products. Still, some researchers say that if the cataracts are in the very early stage, then the ingredient in Can-C and Brite-Eyes (NAC) can reverse them. In fact there are lots of testimonials on the Web from people who said it worked for them, although I have read a few which said it didn't work, probably because the cataract was too far advanced.