Loperamide is the generic name for an over-the-counter and prescription medication used to treat diarrhea. It is sold under such brand names as Imodium, Diamode, Imogen, Kao-Paverin, Imotil and Imperim. It can be used by itself or in combination with other medications to help stop diarrhea. It does this by reducing the speed at which the intestines move food through your system. Bismuth subsalicylate is another OTC anti-diarrhea medication sold under such brand names as Pepto Bismol, Kapectolin, Kaopectate, Diotame, Helidac and Kola-Pectin. Both types of anti-diarrhea medications can produce side effects, but only rarely.
Non-Serious Side Effects
The Mayo Clinic reports there are three potential side effects of loperamide that may occur when you first take the medicine: mouth dryness, drowsiness and dizziness. None of these require medical attention under normal circumstances. However, if you are taking the drug under a doctor's orders and these effects annoy you, alert your doctor who might prescribe a different medication.
Bismuth subsalicylate may cause a dark discoloration of feces and your tongue, according to Drugs.com. While these side effects can be alarming, they are temporary and non-serious.
Serious Side Effects
Anti-diarrhea medications such as loperamide can cause some serious side effects. These are rare, but might occur in some people taking either the prescription or OTC varieties of the medication. They include severe pain in the stomach, abdominal bloating, vomiting, constipation, nausea and a decrease in or loss of your normal appetite.
Bismuth subsalicylate can cause many more serious side effects such as anxiety, confusion, depression, speaking difficulties, thirstiness, severe headaches or drowsiness, spasms in the muscles, severe vomiting that continues, rapid breathing, trembling and weakness in the muscles. It also may cause uncontrollable movements of the body, continual buzzing or ringing in the ears and vision problems.
According to the Mayo Clinic, a rash on the skin might develop if you have an allergic reaction to the medication. Because allergic reactions can be serious, call your doctor immediately if you notice a rash or experience itching that you did not have before you took the drug.
Bismuth subsalicylate also can also cause an allergic reaction, the side effects of which can be serious, requiring emergency medical attention. Symptoms include hives or a rash, chest tightness, itching and facial swelling that might include the tongue, lips and mouth.