Imodium (loperamide) usually starts to work within about 1 hour, with many people noticing improvement in diarrhea between 30 minutes and 2 hours after a dose.

Onset and duration

• Most guidance for loperamide says it begins improving diarrhea within roughly 1 hour, though some people feel relief a bit sooner and others closer to 2 hours.

• The effect can last several hours and, in many adults, provides symptom control for much of the day, depending on dose and individual response.

When to seek help

• If your diarrhea is not improving at all after 48 hours of using over‑the‑counter loperamide as directed, you should stop taking it and contact a doctor, as many guidelines warn against longer unsupervised use.

• Seek urgent medical care sooner if you have high fever, blood in the stool, severe abdominal pain, or signs of dehydration such as dizziness, confusion, or very little urine, because these can indicate a more serious condition where loperamide may not be appropriate.