Loperamide
- Class: Antidiarrheal
- Used for: diarrhea
- Say it: loh-PER-uh-mide
- Forms: capsule, tablet, oral liquid
LOPERAMIDE makes the racing gut LOPE along slowly instead. More water is reabsorbed and the stools firm up.
It is an opioid that works on gut receptors only, because a pump keeps it out of the brain. Never use it in bloody diarrhoea with fever — slowing the gut there risks toxic megacolon.
It acts on the same mu receptors as morphine, but on the bowel wall only — P-glycoprotein pumps it straight back out of the brain. Constipation without analgesia or euphoria, by design.
Side effects
Common: constipation, dizziness, stomach cramps
Serious: arrhythmia at high doses, toxic megacolon
Typical dose
4 mg initially, then 2 mg after each loose stool; maximum 16 mg daily
Maximum 16 mg daily. The first dose is double the rest — 4 mg, then 2 mg after each loose stool.
Check yourself
Why does loperamide not cause euphoria at normal doses?
- P-glycoprotein pumps it out of the brain, so it acts only on gut opioid receptors
- It binds a receptor found only in the intestine
- It is not absorbed from the gut at all
- It is chemically unrelated to the opioids
Show answer
A. P-glycoprotein pumps it out of the brain, so it acts only on gut opioid receptors
Loperamide is a genuine mu agonist. Its safety comes from distribution, not from a different target — and overwhelming that barrier with huge doses is exactly what makes high-dose misuse so dangerous.
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