Side effects associated with the antidiarrheal medication bismuth subsalicylate are rare, although some patients may experience a darkish tongue or grayish-black stools until they stop taking the medication. Patients who use bismuth subsalicylate should notify a physician if they experience any of the following:

• Severe constipation
• Severe or continuing diarrhea
• Severe or continuing nausea and vomiting
• Severe or continuing stomach pain
• Anxiety
• Loss of hearing
• Confusion
• Difficulty speaking or slurred speech
• Dizziness or lightheadedness
• Severe drowsiness
• Fast or deep breathing
• Severe or continuing headache
• Increased sweating
• Increased thirst
• Mental depression
• Muscle spasms, particularly in the face, neck and back
• Muscle weakness
• Ringing or buzzing in the ears
• Trembling
• Uncontrollable flapping movements of the hands (especially in elderly patients)
• Other uncontrolled body movements
• Vision problems

Side effects are also rare in those using loperamide, although patients may experience dryness of mouth, dizziness or drowsiness. However, patients who are taking loperamide should consult a physician if they experience any of the following side effects:

• Bloating
• Constipation
• Severe stomach pain with nausea and vomiting
• Loss of appetite
• Skin rash

Other side effects associated with antidiarrheals include:

• Abdominal cramps
• Central nervous system (CNS) effects such as drowsiness and headache
• Rapid heart rate (tachycardia)
• Prolonged dilation of the pupil (mydriasis)
• Dry mouth
• Urine retention
• Skin itchiness or rash