Side effects of drinking mouthwash include organ failure, blindness and death, according to Alcohol Rehab Advice. The alcohol in mouthwash is typically denatured alcohol, so it is not fit for consumption; it can also be methyl alcohol, which is poisonous.
Some people misuse mouthwash because it contains alcohol that can cause drunkenness, but it can also cause serious problems, including toxicity and even death. Alcohol Rehab Advice notes that even ingesting a small amount of mouthwash can cause problems; ingesting large amounts can lead to serious problems.
There are other ingredients in mouthwash that can be harmful to human health. It can contain hydrogen peroxide, which can damage the gastrointestinal tract and cause symptoms like vomiting, diarrhea, nausea and upset stomach. Phenolic compounds in some mouthwashes, including thymol, eucalyptol and menthol that can be toxic in large amounts.
Alcohol Rehab Advice cites a case study in which a 45-year-old man died as a result of multiple organ failure due to consuming mouthwash. The man succumbed to organ failure despite medical intervention, including mechanical ventilation and dialysis. The study concluded that it was the phenolic compounds in the mouthwash that ultimately caused the failure of the patient's organ system and his death.