Omeprazole side effects and how to avoid them

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Omeprazole (brand name: Prilosec) is a prescription and over-the-counter (OTC) medication that reduces stomach acid. It is part of a class of drugs called proton pump inhibitors (PPIs) and is most often taken as a capsule or tablet. Omeprazole is used to treat symptoms of gastroesophageal reflux disease (GERD), stomach and duodenal ulcers, and other conditions that cause excess stomach acid. 

Although omeprazole can be purchased without a prescription, the drug has several side effects, some quite serious. Knowing the potential side effects, warnings, contraindications, and drug interactions can help determine if omeprazole is the right drug to take.

RELATED: Learn more about omeprazole

Common omeprazole side effects

The most common side effects of omeprazole are:

• Headache
• Abdominal pain
• Nausea
• Diarrhea
• Vomiting
• Gas

Omeprazole is sometimes combined with the antibiotics clarithromycin and amoxicillin to treat H. pylori, an infection linked to gastritis (irritation of the stomach lining) and stomach ulcers. The most common adverse effects of combining omeprazole with these medications are:

• Diarrhea
• Taste changes
• Headache
• Tongue discoloration
• Nasal congestion

Omeprazole and constipation

Omeprazole may cause constipation in some people, although it’s less common than other digestive side effects like diarrhea and gas. In clinical trials of over 3,000 patients, constipation occurred in 2% of patients. However, it wasn’t reported to be a severe side effect. It might appear within the first few days of treatment and subside as the body adjusts to the drug.

Omeprazole and weight gain

Significant weight gain has been linked with years-long use of omeprazole and other PPIs to treat heartburn or GERD symptoms. The reasons are unclear, but it is thought to be due to increased appetite when symptoms are better controlled.

Serious side effects of omeprazole

Serious side effects are rare for omeprazole but may include:

• Severe diarrhea: C. difficile is a bacterial infection of the colon that can cause severe diarrhea and fever.
• Liver disease: Omeprazole can alter liver function and sometimes lead to liver disease or liver failure.
• Lupus: Omeprazole may cause the onset or worsening of lupus erythematosus, an autoimmune condition marked by rash and skin redness.
• Allergic reactions: Hypersensitivity reactions can be mild to severe, including anaphylaxis, rapid skin swelling (angioedema), severe skin reactions, trouble breathing, and swelling in the kidney’s filtration tubes (interstitial nephritis).

These side effects are often linked to long-term use or high doses of omeprazole. Because of this, the prescribing information states that omeprazole should be used at the lowest effective dose for the shortest period of time. 

Other serious side effects may include:

• Bone loss: Used long-term, omeprazole can reduce the absorption of calcium. The body balances this loss by pulling calcium from the bones, leading to osteoporosis and an increased risk of bone fractures. Patients taking omeprazole continuously over the long term (one year or longer) may need to take calcium supplements and/or prescription medication to help prevent osteoporosis and the risk of fractures.
• Low magnesium: Long-term use of omeprazole can also lower magnesium levels in the body. Low magnesium (hypomagnesemia) can lead to muscle cramps, an irregular heartbeat, tremors, or seizures.
• Growths: Omeprazole has been linked to fundic gland polyps, which are usually benign, small growths along the stomach lining. Rarely, in patients with Zollinger-Ellison syndrome, omeprazole has also been linked to slow-growing tumors (carcinoids) in the duodenum, the first part of the small intestine.
• Low vitamin B12: Using omeprazole or other acid-suppressing medications daily for long periods of time (usually longer than 3 years) may reduce the absorption of vitamin B12 due to low stomach acid. Although rare, vitamin B12 deficiency has been reported in people taking omeprazole long-term.

Omeprazole and cancer

There is a popular notion that omeprazole and other PPIs may increase the risk of stomach cancer. Research on the association of omeprazole with stomach cancer is mixed, with some studies showing omeprazole (or any PPI) can increase the risk of stomach cancer. 

More importantly, omeprazole could mask the symptoms of stomach cancer. In other words, people could start taking omeprazole for heartburn, but the symptoms may be caused by a malignancy. Symptoms such as frequent heartburn should always be evaluated by a healthcare provider.

Omeprazole side effects by dosage

A higher dose of omeprazole may lead to greater side effects. For example, a dose of 40 mg of omeprazole may lead to more gastrointestinal side effects like stomach discomfort, diarrhea, and gas. The risk of serious side effects may be increased not only with higher doses but also with long-term use of high doses. For this reason, omeprazole is typically reserved for short-term use.

How long do omeprazole side effects last?

The body clears omeprazole in a few hours, so many mild side effects will fade in that time. However, the effects of omeprazole on the stomach lining typically last for three or more days, which means some side effects may linger for a few days after stopping omeprazole. 

Side effects caused by combining omeprazole with antibiotics, such as taste changes or tongue discoloration, usually resolve a few days after the antibiotics are discontinued. Serious side effects associated with omeprazole, however, like bone loss, liver disease, or kidney problems, may take longer to get better. All side effects should be reported to your healthcare provider.

Omeprazole contraindications & warnings

Omeprazole is an effective medication that has a low incidence of possible side effects when used in the short term. However, omeprazole may not be for everyone, particularly when used over the long term.

Dependency

Chronic use of omeprazole can lead to serious and debilitating side effects. In particular, people taking omeprazole for a long time may develop a kind of physical dependency since the body gets used to decreased acid production. Stopping the medication could cause the stomach to create more acid than usual, leading to a rebound effect and a return of acid reflux and heartburn symptoms. 

Allergies

Omeprazole should not be taken by anyone with severe hypersensitivity to omeprazole or any of the inactive ingredients of this medication.

People with liver problems

Omeprazole is processed by the liver. Patients with liver problems can generally take omeprazole (if approved by a healthcare provider), but the dosage may be lower than usual.

People of Asian descent

People of Asian descent may have an increased risk of dementia from proton pump inhibitors such as omeprazole. People of Asian descent are also less likely to have the gene variants that break down omeprazole quickly. The prescribing information for omeprazole recommends a lower dose in these patients.

Children

Prescription omeprazole is approved to treat GERD symptoms and erosive esophagitis in children who are 1 to 16 years of age. OTC omeprazole should not be given to children. If the liquid formulation (packets for oral suspension) is not available, the medication can be compounded by a compounding pharmacy. The contents of a capsule may also be mixed with a tablespoon of applesauce and immediately consumed, along with a glass of water.

Older adults

In the initial clinical trials, omeprazole had the same safety record in older adults as it does for other adults. However, more recent studies suggest that omeprazole may come with an increased risk of certain side effects in older adults, such as bone loss, kidney problems, and possible dementia.

Pregnancy and breastfeeding

There are no definitive studies on the safety of omeprazole use during pregnancy. The prescribing information advises that pregnant women should use omeprazole only if it’s absolutely necessary. 

Omeprazole may be present in breast milk in small amounts and is not expected to cause harm to a nursing infant. However, it’s important to consult a healthcare provider about whether to discontinue omeprazole.

Omeprazole interactions

In general, food does not affect the absorption or effectiveness of omeprazole. However, since the goal is to reduce stomach acid, it’s best to avoid foods that overstimulate stomach acid secretion, such as spicy foods, fatty foods, sodas, alcohol, and coffee. 

Like many drugs, omeprazole can interact with other medications or substances. The following medicines may interact with omeprazole: 

Antiretrovirals

Omeprazole is contraindicated while taking rilpivirine, an HIV medication, because omeprazole can reduce its absorption. As a result, omeprazole can decrease the effectiveness of rilpivirine. Omeprazole may need to be avoided with other antivirals like atazanavir and nelfinavir because of similar effects. Taking omeprazole with saquinavir, however, could increase the levels of saquinavir and lead to toxic effects of the antiviral. 

Drugs that rely on stomach acid for absorption

Because omeprazole reduces stomach acidity, it may decrease how well some medications are absorbed, which may make them less effective. Examples include: 

• Iron salts 
• Antifungals such as Nizoral (ketoconazole) or Sporanox (itraconazole)
• Cancer drugs such as Tarceva (erlotinib), Sprycel (dasatinib), and Tasigna (nilotinib) 
• Synthroid (levothyroxine)
• Cellcept (mycophenolate mofetil)

Blood thinners and antiplatelets

Many people take blood thinners to help treat blood clots. However, omeprazole interacts with the blood thinner warfarin and could potentially cause abnormal bleeding. If you are on omeprazole and warfarin, your doctor will monitor you closely and may need to change the dosage of your medication(s). 

Omeprazole also interacts with the antiplatelet agents Plavix (clopidogrel) and Pletal (cilostazol).  Plavix should not be taken with omeprazole. If you take Pletal with omeprazole, the dosage of Pletal may need to be adjusted. 

Drugs whose levels increase when taken with omeprazole

Omeprazole can increase the toxicity and risk of side effects of some prescription drugs by either increasing their absorption or slowing down the body’s metabolism of the drug. 

These drugs include:

• Trexall (methotrexate)
• Prograf (tacrolimus)
• Dilantin (phenytoin)
• Valium (diazepam)
• Lanoxin (digoxin)
• Celexa (citalopram)

These drugs can generally be taken with omeprazole, but a healthcare professional may need to monitor therapy and reduce doses if necessary.

Drugs that decrease omeprazole’s effectiveness

Some drugs speed up the body’s metabolism of omeprazole, reducing its effectiveness. These include:

• The antibiotics Rifadin (rifampin), Priftin (rifapentine), and Mycobutin (rifabutin)
• Some antiviral drugs, such as Norvir (ritonavir)
• Cystic fibrosis drugs Orkambi (lumacaftor-ivacaftor)
• St. John’s wort

Diuretics (water pills)

Taking diuretics with omeprazole can increase the risk of low magnesium. Therapy may need to be monitored or modified.

How to avoid omeprazole side effects

When taken as directed for a limited time, omeprazole has minimal side effects. A few tips can help keep side effects to a minimum: 

1.  Take omeprazole as directed

Take the daily dose as prescribed at the time prescribed. Prilosec OTC should be taken in the morning before breakfast. For prescription omeprazole, the prescribing doctor or other healthcare professional will specify a time of day to take the medication. Don’t increase or decrease the dose on your own, and don’t take a double dose in place of a missed dose. The medicine must be taken daily over the full period to realize its full benefits. 

2.  Avoid taking omeprazole long-term

Only take omeprazole for the short-term, anywhere from 10 days to eight weeks. Very few medical conditions require omeprazole to be taken for longer periods. Continual use of omeprazole not only raises the risk of side effects in general, but it also raises the risk of more serious side effects. If the medicine seems to require long-term use, talk to a healthcare provider about alternative drugs. 

3.  Tell your doctor about all your medical conditions and medications

Because of the risk of side effects, you should tell your doctor about:

• Any physical conditions you may have, particularly 
  • Chronic chest pain
  • Persistent nausea, vomiting, stomach pain, or unexplained weight loss
  • Low levels of magnesium or calcium
  • Liver or kidney problems
  • Pregnancy or breastfeeding
• All prescription medications, OTC drugs, herbal remedies, and dietary supplements you’re taking

4.  Talk to a healthcare professional before taking OTC omeprazole

Omeprazole can be easily purchased without a prescription. Still, because of the risk of overuse, physical dependency, and side effects, seek medical advice from a healthcare professional before taking OTC omeprazole. Dietary and lifestyle changes may also need to be considered.

5.  Take omeprazole 30–60 minutes before eating

Chances are, the doctor’s prescription, medication guide, or package will have an instruction that reads, “Take before a meal.” The general practice is to take omeprazole 30 to 60 minutes before eating.

6.  Avoid acid-raising foods and drugs

Many foods or drugs stimulate the stomach lining to increase acid production. These include spicy foods, fried foods, fatty meats, cheeses, peppers, citrus fruits, chocolate, coffee, alcohol, soda pop, aspirin, peppermint, and some mineral supplements. Eating spicy foods will not increase the risk of omeprazole side effects, but they may increase the amount of acid in the stomach and blunt the effects of the medicine.

How to treat side effects of omeprazole

Most side effects of omeprazole aren’t severe enough to require medical attention. They can often be managed at home in different ways and only last temporarily. For digestive side effects like nausea and gas, it can be helpful to stay hydrated, eat smaller meals, and avoid triggering foods. In some cases, short-term OTC medications may be used, but it’s best to consult a doctor or pharmacist first. 

Seek medical help for any serious or unusual symptoms, such as severe diarrhea, fever, persistent vomiting, joint pain, unusual tiredness, or signs of a severe allergic reaction, such as rash or difficulty breathing. These could indicate more serious side effects of omeprazole that may require medical attention.

Bottom line: Is omeprazole safe?

Omeprazole is generally safe to take when taken as directed. Those who take omeprazole at high doses for longer periods are more likely to experience serious side effects. For those who take omeprazole at the lowest effective dosage, most side effects are short-term and mild. 

Expert takeaway

Gerardo Sison, Pharm.D., and a member of the SingleCare Medical Board, says, “Most side effects can be avoided by using omeprazole for the shortest duration possible and at the lowest effective dose. Don’t rely on OTC omeprazole for persistent heartburn without first consulting a healthcare provider. Long-term daily use is linked to more serious side effects.”