Vinegar's key ingredient acetic acid has its side effects, sometimes causing heartburn and bad breath. When used in larger quantity, too much acidity on the stomach can have negative effects such as kidney failure and severe internal burns as once reported from rupture of red blood cells when a woman who attempted suicide by drinking about 400 millilters of 25 percent acetic acid-- roughly the same amount you'd find in a quart of strong vinegar.
Another report tells of a cider vinegar fan who developed hypokalemia (low potassium levels), hyperreniemia (a condition caused by overactive kidneys that can lead to high blood pressure and other problems), and osteoporosis.
And vinegar pills have a list of adverse effects such as: irritability, nervousness, and papitations and less frequently anorexia, constipation, gastrointestinal irritation, headaches, "hypersecretory conditions," vertigo, and vomiting.
Staying within small doses will maintain a healthy and safe digestive system.