The effects of drinking hydrogen peroxide vary depending on the amount consumed and its concentration. Consumption of small quantities of dilute hydrogen peroxide can have minor, if any, clinical effects, while drinking larger amounts or higher concentrations has caused fatalities. According to the National Institutes of Health, common hydrogen peroxide concentrations range from 3 percent, which is used as a disinfectant, to 90 percent, which is used as rocket fuel.
At low concentrations, small amounts of hydrogen peroxide can cause nausea, vomiting and minor erosion of the mucous membranes of the mouth and gastrointestinal tract, states the NIH. Higher concentrations, such as the 35-percent "food grade" hydrogen peroxide, which is sometimes consumed for its purported benefits in treating cancer, AIDS and dementia, can easily be fatal.
In high-dose cases of hydrogen peroxide poisoning, large amounts of oxygen can be released during digestion that can create a gas embolism in the patient's blood, gastric wall or brain. When the embolism occurs in the brain, the symptoms resemble those of an ischemic stroke and require emergency treatment. The NIH notes that, while ingestion of 3-percent solution is rarely lethal, consumption of the more concentrated 35-percent solution has the potential to kill by multiple mechanisms.