Lansoprazole is a proton pump inhibitor (PPI) used to reduce stomach acid. Sold under the brand name Prevacid, it treats conditions caused by excess acid, including GERD, stomach ulcers, duodenal ulcers, and erosive esophagitis. It’s also used alongside antibiotics to clear H. pylori infections. Lansoprazole is available both over the counter and by prescription.
How Lansoprazole Works
Your stomach lining contains millions of tiny acid-producing cells called parietal cells. These cells use a specialized pump (the hydrogen-potassium pump) to push acid into your stomach. Lansoprazole is a prodrug, meaning it’s inactive when you swallow it. Once it reaches the acidic environment inside those parietal cells, the acid activates the drug into its working form. The activated drug then locks onto the pump permanently by forming a chemical bond, shutting it down.
Because the bond is permanent, each dose disables acid pumps for the life of that pump protein. Your body makes new pumps over time, which is why you take it daily. A single dose suppresses acid for more than 24 hours, even though the drug itself clears from your bloodstream in under two hours. Full acid suppression builds over several days of consistent use.
GERD and Heartburn
The most common reason people take lansoprazole is gastroesophageal reflux disease, or GERD. When stomach acid repeatedly washes up into the esophagus, it causes the burning chest pain most people call heartburn. Lansoprazole treats both the symptoms and the underlying damage.
For straightforward GERD symptoms like heartburn, the typical course is 15 mg once daily for up to 8 weeks. If acid reflux has already damaged the lining of the esophagus (a condition called erosive esophagitis), the dose goes up to 30 mg once daily for up to 8 weeks. About 5 to 10% of people with erosive esophagitis don’t fully heal in that window and may need a second 8-week course. Once healing is confirmed, lansoprazole can also be used as a maintenance treatment to keep erosive esophagitis from returning.
Stomach and Duodenal Ulcers
Lansoprazole heals ulcers in two locations: the stomach itself (gastric ulcers) and the duodenum, the first section of the small intestine just beyond the stomach. By dramatically reducing acid levels, it gives the damaged tissue a chance to repair.
For active duodenal ulcers, treatment is typically 30 mg daily for 4 weeks. Active gastric ulcers generally require 30 mg daily for up to 8 weeks. After a duodenal ulcer heals, lansoprazole can be continued at a lower maintenance dose to prevent it from coming back, though controlled studies of this approach haven’t extended beyond 12 months.
Ulcers From Pain Medications
Nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen and naproxen are a common cause of stomach ulcers, especially with long-term use. Lansoprazole has two roles here. It can heal NSAID-associated gastric ulcers in people who need to keep taking their NSAID, with treatment lasting up to 8 weeks. It can also be used preventively to reduce the risk of developing an ulcer in the first place if you have a history of gastric ulcers and need ongoing NSAID therapy.
H. Pylori Infection
H. pylori is a bacterium that burrows into the stomach lining and is responsible for many duodenal ulcers. Lansoprazole alone won’t kill it, but it plays a critical role in the combination therapy that does. The standard approach is triple therapy: lansoprazole paired with two antibiotics (amoxicillin and clarithromycin), all taken twice a day for 10 to 14 days. Eradicating the infection significantly reduces the chance of the ulcer coming back.
For people who are allergic to clarithromycin or carry a resistant strain, a dual therapy option pairs lansoprazole with amoxicillin alone. The lansoprazole serves double duty in these regimens: it reduces acid to help the ulcer heal while also creating a less acidic environment where the antibiotics work more effectively.
Prescription vs. Over-the-Counter
Lansoprazole is one of the few PPIs available without a prescription. The OTC version is intended for frequent heartburn, defined as heartburn occurring two or more days per week. It’s designed for short-term, self-directed use following the instructions on the label.
The prescription version covers the full range of conditions described above, often at higher doses or for longer treatment courses. A prescription also allows your doctor to tailor the dose to your specific condition, whether that’s a 15 mg daily dose for mild GERD symptoms or 30 mg for an active ulcer. The distinction matters because conditions like gastric ulcers and erosive esophagitis need medical monitoring to confirm healing.
How Quickly It Works
You won’t get the instant relief you’d get from an antacid tablet. Lansoprazole starts working within the first few hours of your first dose, raising the pH (lowering the acidity) inside your stomach. But it reaches its full acid-suppressing potential after about a week of daily use, as it progressively disables more and more acid pumps. During the first-hour window after a dose, absorption is already underway, but the cumulative effect of daily dosing is what delivers the real therapeutic benefit.
Take it before eating, ideally 30 minutes before a meal. Food in the stomach can reduce how much of the drug gets absorbed.
Common Side Effects
Most people tolerate lansoprazole well. The most frequently reported side effects are diarrhea, abdominal pain, and nausea. These are generally mild and tend to resolve on their own. Headache and constipation also show up in clinical trial data but are less common.
When lansoprazole is taken as part of triple therapy with antibiotics for H. pylori, side effects are more common simply because you’re taking three drugs at once. Diarrhea and taste changes are particularly common with that combination.
Risks With Long-Term Use
Short courses of lansoprazole (4 to 8 weeks) carry minimal risk for most people. The concerns center on extended use over months or years. Suppressing stomach acid for prolonged periods can interfere with your body’s ability to absorb certain nutrients, particularly magnesium, calcium, and vitamin B12. Low magnesium can cause muscle cramps, irregular heartbeat, and seizures in severe cases. Reduced calcium absorption has been linked to a modest increase in bone fracture risk, particularly hip, wrist, and spine fractures in older adults.
There’s also an association between long-term PPI use and a slightly elevated risk of kidney problems and a type of gut infection caused by the bacterium C. difficile, which thrives when stomach acid isn’t keeping bacteria in check. These risks are why doctors generally recommend using the lowest effective dose for the shortest time necessary, and periodically reassessing whether you still need the medication.
Interactions With Other Medications
Lansoprazole can affect how other drugs are absorbed or metabolized. Because it raises stomach pH, drugs that need an acidic environment to dissolve properly may not work as well. This includes certain antifungal medications and some HIV treatments.
One interaction worth knowing about involves the blood thinner clopidogrel. Both drugs are processed by the same liver enzyme. The European Society of Cardiology considers the interaction risk with lansoprazole “intermediate,” less concerning than with omeprazole but not as clean as with pantoprazole. At the standard 30 mg dose, lansoprazole does not significantly reduce clopidogrel’s effectiveness. At higher doses (60 mg), it can modestly lower peak blood levels of clopidogrel by about 18%. If you’re on clopidogrel and need a PPI, your doctor may prefer pantoprazole, but standard-dose lansoprazole is generally considered acceptable.