welcome to healthcaremagicHydrogen peroxide
treatment for cancer is not STANDARD treatment. According the American Cancer Society, there is no scientific evidence that hydrogen peroxide is a safe, effective or useful cancer treatment, .Its only use is as a surface disinfectant.
Moreover it is a toxic compound . Hydrogen peroxide ingestion can also result in chemical burns in the throat and severe poisoning
It can be cause of his stomach problems.
So my advise is to immediately stop this unproven and potentially toxic treatment.