Short answer: Loperamide (Imodium) is an over-the-counter diarrhea medicine that acts on opioid receptors in the gut. At label doses it is safe and does not reach the brain. Taken in very large amounts, often to ease opioid withdrawal, it can cause dangerous heart rhythm problems, cardiac arrest, and death.
Key takeaways
- What it is: Loperamide is a peripheral opioid receptor agonist (antidiarrheal) and not a federally controlled substance.
- Main uses: Diarrhea.
- Timing: effects start in 1 to 3 hours and last up to 24 hours.
- Most dangerous mix: Methadone, antiarrhythmics, some antibiotics and antipsychotics, which can cause stacked QT prolongation and heart rhythm risk.
- Naloxone: it partly reverses an overdose (breathing, not the heart).
- Dependence risk: Low at label doses; high with misuse.
- Legal route: sold without a prescription; follow the Drug Facts label.
What is loperamide?
Loperamide slows the movement of the gut and treats diarrhea. At normal doses a transporter called P-glycoprotein pumps it out of the brain, so it has no opioid effects on mood or breathing.
Some people take tens or hundreds of times the label dose to self-treat opioid withdrawal or to get high. The FDA warned in 2016 that such doses had caused serious heart problems and deaths, and asked makers to limit package sizes.
Quick facts
| Fact | Loperamide |
|---|---|
| Generic name | Loperamide hydrochloride |
| Brand names | Imodium A-D, Imodium Multi-Symptom Relief |
| Drug class | Peripheral opioid receptor agonist |
| US legal status | Over the counter; not controlled |
| Approved uses | Diarrhea, including travelers' diarrhea |
| Forms | Capsules, tablets, liquid |
| Maximum OTC dose | 8 mg a day for adults |
| Half-life | About 9 to 14 hours |
| Packaging limits | Sold in blister packs of limited size since 2019 to deter misuse |
How long does loperamide last?
- Starts working: 1 to 3 hours
- Effects last: Up to 24 hours
- Half-life: About 9 to 14 hours
Timing varies with the dose, the form, how it is taken, liver and kidney function, age, and other drugs taken at the same time.
What are the biggest risks of loperamide?
Common side effects at label doses include constipation, dizziness, and stomach cramps.
Heart rhythm problems: high doses lengthen the heart's QT interval and widen the QRS complex, causing fainting, torsades de pointes, ventricular tachycardia, and cardiac arrest. These can be hard to treat and deaths have occurred.
Children: in young children, even modest overdoses can cause severe constipation, drowsiness, and slowed breathing.
Warning: Taking more than the label dose to manage opioid withdrawal is dangerous. Buprenorphine and methadone treat withdrawal and opioid use disorder safely.
What should you never mix with loperamide?
| Combined with | What happens | Guidance |
|---|---|---|
| Methadone, antiarrhythmics, some antibiotics and antipsychotics | Stacked QT prolongation and heart rhythm risk | Avoid at high doses |
| Itraconazole, ketoconazole, clarithromycin, ritonavir, quinidine, gemfibrozil | Raise loperamide levels several-fold | Avoid combining with high doses |
| Cimetidine and P-glycoprotein inhibitors used to boost effects | Loperamide enters the brain; toxicity | Dangerous |
| Opioids | Constipation and, with misuse, sedation | Use caution |
Check any combination with the DoseUses combination checker or ask a pharmacist.
What are the signs of a loperamide overdose, and what should you do?
Loperamide overdose can cause fainting, a fast or irregular heartbeat, seizures, and cardiac arrest, sometimes days after the last dose. It can also cause sleepiness and slowed breathing.
If someone may have taken too much
- Call 911 for fainting, a seizure, chest pain, a racing or irregular heartbeat, confusion, or if the person cannot be woken.
- If the person collapses and is not breathing normally, start CPR and use an AED if one is available.
- Give naloxone if opioids could be involved. It is safe even if they are not.
- For advice when the person is awake and stable, call Poison Help at 1-800-222-1222 (US, free, 24 hours). Bring the product packaging to the hospital.
What is loperamide withdrawal like, and how long does it last?
People who take very high doses every day develop opioid-like dependence and withdrawal when they stop.
- 12 to 48 hoursEarly symptomsAnxiety, sweating, runny nose, yawning, muscle aches, and diarrhea.
- Days 2 to 5PeakStomach cramps, nausea, goosebumps, poor sleep, and cravings.
- 1 to 2 weeksLingering symptomsLow mood and cravings may persist.
See the withdrawal timelines and the full loperamide withdrawal guide.
Is loperamide legal?
Loperamide is sold over the counter without a prescription. Since 2019, the FDA has asked makers to sell it in blister packs with a limited number of doses to make misuse harder.
- Cost: generic loperamide is inexpensive at pharmacies and grocery stores.
- Prescription strengths: clinicians can prescribe it for chronic diarrhea, with a maximum of 16 mg a day.
- Ask a pharmacist: a pharmacist can check whether it is safe with your other medicines and health conditions.
Outside the United States
| Country | Status |
|---|---|
| United Kingdom | Pharmacy and general sale medicine, with pack-size limits |
| Canada | Non-prescription medicine |
| International | Not under UN control |
Frequently asked questions about loperamide
Is Imodium an opioid?
Yes, chemically, but at label doses it stays in the gut and does not affect the brain or breathing.
How much loperamide is too much?
More than 8 mg a day without medical advice. Heart problems have been reported at doses of roughly 70 mg a day and higher.
Can loperamide help opioid withdrawal?
Label doses can ease diarrhea from withdrawal, but taking large amounts to relieve other symptoms is dangerous. Buprenorphine and methadone are safer and effective.
Does loperamide show up on a drug test?
Not on standard opioid screens.
Why do pharmacies sell Imodium in small packs?
The FDA asked makers to limit package sizes in 2019 to reduce misuse at very high doses.
Sources
- Imodium (loperamide) prescription information, DailyMed, US National Library of Medicine.
- FDA Drug Safety Communication: FDA warns about serious heart problems with high doses of the antidiarrheal medicine loperamide (Imodium), US Food and Drug Administration, 2016.
- BeSafeRx: Your Source for Online Pharmacy Information, US Food and Drug Administration.
- International drug control conventions, United Nations Office on Drugs and Crime.
This guide summarizes the sourced DoseUses Loperamide profile, written from FDA labels, DEA rules, and federal health agencies. It is educational and is not medical advice. Last updated October 5, 2026.
