Imodium (loperamide) typically begins to work within about 1 hour after taking the recommended dose. Most people notice a reduction in the frequency of bowel movements and improvement in stool consistency shortly after that time. The effect can last several hours, and it helps by slowing down bowel movements to allow more water absorption and firmer stools. However, for the diarrhoea itself to fully subside, it may take 2 to 4 days depending on the cause. Imodium is generally used for short-term relief and should not be taken for more than 48 hours without medical advice.