Pepto-Bismol is considered to be quite safe for short-term use by adults and children who are age 12 or over. When used properly, the only side effect may be a temporary and harmless blackening of the tongue or of the stool. In some cases the medication may work too well, with constipation as a result.
Pepto-Bismol is only recommended for use for a two day period. That therefore makes it a poor choice for regular use as treatment for people who experience chronic diarrhea, common in those with irritable bowel syndrome (IBS). It also makes it a poor choice for people who experience chronic heartburn or acid reflux from gastroesophageal reflux disease (GERD).
Serious side effects of Pepto-Bismol are rare, but not unheard of. For the elderly, any resulting constipation may lead to a bowel blockage. For children and teenagers, as Pepto-Bismol is in the aspirin family, the biggest risk associated with the medicine is the development of Reye’s syndrome, a potentially life-threatening illness. This risk is particularly high for those who have chicken pox, influenza (the flu), or any other type of viral infection.
However, there is a product for children called Children’s Pepto. It does not contain bismuth subsalicylate and thus does not carry the same risk as Pepto-Bismol. Children’s Pepto is designed to treat heartburn and upset stomach in children.