Hydrogen Peroxide might kill cancer cells if it could be fed directly to them, might work pretty well too; but the problem is in the delivery system, as it is for any kind of chemotherapy. Food-grade H2O2 is 35% or so, and is used for disinfecting and bleaching stuff. Works great for that, not least because it’s water soluble and can be rinsed away, and breaks down in the sewer system. At that concentration, it would also disinfect the sewer pipes, and clear out most clogs.
Anything higher than 35% is a bit of a fire risk, since H202 is a monopropellant. Those jetpacks demoed at the county fair and wherever use 100% H202, with a catalyst (I forget what metal), and nothing else. I wouldn’t want to have the 35% around either, unless I were going to use it right away, because, well, it could go up, and the result would not be pretty. Well, in a sense it would be pretty, but the damage wouldn’t be. ;’)
I think the proponents advocate 8 drops a day in a glass of water or some such.