Lansoprazole: what it treats, how to take it, side effects
Last updated September 3, 2026.
Lansoprazole is a proton pump inhibitor - it turns down the stomach's acid production at the source. You may know it as Prevacid, prescription or over the counter. It heals what acid damages - and it is the drug people stay on for years without revisiting why.
What does it treat?
Prescription: GERD and the esophagus damage it causes, ulcers, ulcer prevention in NSAID users, Zollinger-Ellison and other too-much-acid conditions, and H. pylori eradication in combination with antibiotics. Over the counter: frequent heartburn - two or more days a week - in adults, for 14-day courses.
How do you take it?
Once a day before a meal for most uses; twice or three times daily before meals for H. pylori courses of 10 to 14 days. Swallow the capsules whole - or open one and sprinkle the granules on a tablespoon of applesauce, pudding, cottage cheese, yogurt, or strained pears and swallow immediately without chewing. The dissolving tablet goes on the tongue, never broken or chewed. The OTC version: once daily in the morning before eating, 14 days, and no repeat course more often than every 4 months - if heartburn keeps returning on that schedule, that is a doctor conversation, not another box. Missed dose: take it when you remember unless the next one is close; never double up.
Side effects to know
- Common: constipation, nausea, headache, dizziness, diarrhea, and - in men - difficulty achieving or maintaining an erection.
- Serious - call your doctor immediately: allergic signs - rash, hives, itching, swelling of the eyes, face, lips, mouth, throat, or tongue, trouble breathing or swallowing, or hoarseness; blistering, peeling, or bleeding skin with sores on the lips, nose, mouth, or genitals; kidney-pattern signs - changed urination, blood in urine, fatigue, nausea, loss of appetite, fever, rash, or joint pain; irregular, fast, or pounding heartbeat with muscle spasms, uncontrollable shaking, excessive tiredness, lightheadedness, dizziness, or seizures (the low-magnesium pattern); severe watery diarrhea with stomach pain or fever that does not go away (C. difficile pattern); and new or worsening joint pain with a sun-sensitive rash on the cheeks or arms (the lupus pattern).
Who should not take it?
Anyone with a past allergic reaction to a PPI. The long-term conversation is the honest one: people on PPIs - especially high doses or a year or longer - fracture wrists, hips, and spines more often, and can develop fundic gland polyps on the stomach lining. The lowest effective dose for the shortest needed time is the right posture, revisited with your doctor rather than renewed forever on autopilot. If you become pregnant, call your doctor.
When is it an emergency?
Throat swelling, trouble breathing, blistering skin, or seizures is emergency care. For an overdose, call Poison Control at 1-800-222-1222. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
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Common questions
Why do I have to take lansoprazole before a meal?
Proton pumps activate when you eat - the drug needs to be onboard and absorbed when the pumps switch on. MedlinePlus: usually once a day, before a meal, same time every day. Before breakfast is the standard anchor because it covers the day's biggest acid production. Taken after eating, you are shutting pumps that already ran.
Why can't I just stay on it forever if it works?
The long-term ledger: people on PPIs - especially at high doses or past a year - fracture wrists, hips, and spines more often, and can develop fundic gland polyps on the stomach lining, per MedlinePlus. Add the low-magnesium and C. difficile patterns on the serious list. None of this means stop a drug you need; it means the need gets re-evaluated - many people step down or off successfully with a plan, and some genuinely need it long-term. That is a decision, not a default.
Why is severe diarrhea on the warning list for an acid pill?
Stomach acid is a defense against swallowed bacteria, including C. difficile - turn the acid down for months and the gut's door stands more open. The pattern that gets a call: severe, watery diarrhea with stomach pain or fever that does not go away, even weeks after the fact. It is treatable, but it needs the right diagnosis, not an anti-diarrheal.
Why did my doctor mention my bones?
The fracture signal: wrist, hip, and spine fractures run higher in long-term, high-dose PPI users. If you are on lansoprazole past a year, bone-protective habits - calcium, vitamin D, weight-bearing exercise - belong in the plan, and your doctor may check your magnesium too, since the heartbeat-spasm-shaking pattern on the serious list is low magnesium announcing itself.
Why can't I chew the capsule or crush the tablet?
The granules are enteric-coated to survive stomach acid - the drug itself is destroyed by acid before it can work. Chewing or crushing breaks the armor. If swallowing is hard, the label-approved move is opening the capsule onto a tablespoon of applesauce, yogurt, or similar and swallowing immediately without chewing - or the dissolving tablet on the tongue.
What happens if I miss a dose of lansoprazole?
Take it as soon as you remember, unless it is almost time for the next one - then skip it and never double up. One missed dose means one day of possibly returning symptoms, not a setback. The before-breakfast anchor is what keeps the question rare.