| Drug class |
Opioid receptor agonist – but it doesn’t cross the blood‑brain barrier at therapeutic doses, so it doesn’t produce central opioid effects. |
| Primary use |
Relief of acute non‑infectious diarrhea, chronic diarrhea (e.g., irritable bowel syndrome, inflammatory bowel disease) when other treatments have failed. |
| Typical OTC dosing |
• Adults & adolescents ≥12 yrs: 0.5 mg (one 2 mg capsule or 2 mg tablet) after first loose stool, then 0.5 mg after each subsequent stool
• Maximum: 8 mg/day (no more than 4 mg on the first day).
• Children 6‑11 yrs: 0.25 mg after first loose stool, then 0.25 mg after each subsequent stool (max 4 mg/day).
• Children <6 yrs: Not approved; use only under pediatrician’s guidance. |
| Prescription dosing |
Often 4 mg/day divided (e.g., 2 mg twice daily) for chronic diarrhea, titrated up to 16 mg/day as needed. |
| Mechanism of action |
Binds to μ‑opioid receptors in the gut wall, reducing intestinal motility and increasing fluid absorption, thereby shortening stool frequency and improving consistency. |
| Onset / Duration |
Onset ~1–3 hrs after ingestion; peak effect ~6 hrs; effects last ~12 hrs. |
| Common side effects |
Constipation, abdominal cramping, nausea, dry mouth, dizziness. |
| Serious but rare |
• Severe constipation or fecal impaction (especially in those with bowel obstruction or ileus).
• Rarely, colonic pseudo‑obstruction (Ogilvie’s syndrome).
• Rare cardiac arrhythmias (QT prolongation) in high doses or with other QT‑prolonging drugs. |
| Contraindications |
• Mechanical bowel obstruction, ileus, colonic pseudo‑obstruction.
• Severe liver disease (risk of drug accumulation).
• Use with caution in patients on CYP3A4 inhibitors (see interactions). |
| Drug interactions |
• CYP3A4 inhibitors (e.g., ketoconazole, clarithromycin, ritonavir): increase loperamide levels → risk of constipation & cardiac toxicity.
• CYP3A4 inducers (e.g., rifampin, carbamazepine): decrease loperamide efficacy.
• Other opioids: additive GI effects.
• Tizanidine, carbamazepine: may increase side‑effect profile. |
| Warnings & Precautions |
• Do not exceed 8 mg/day unless under medical supervision.
• Avoid in patients with known or suspected intestinal obstruction.
• Use with caution in renal impairment (loperamide is excreted renally).
• Report any persistent abdominal pain or signs of obstruction (distension, vomiting). |
| Pregnancy / Lactation |
Classified B (animal studies show no risk, but limited data). Generally considered safe for short‑term use if benefits outweigh risks; discuss with provider. |
| Special populations |
• Elderly: increased sensitivity to constipation; use lowest effective dose.
• Patients with hepatic dysfunction: monitor for accumulation. |