Omeprazole (Prilosec, Prilosec OTC) is a generic medication that’s used to treat conditions caused by a high stomach acid level. It comes as a prescription and over-the-counter (OTC) drug.

Prescription omeprazole is used to:

OTC omeprazole is used to treat heartburn in adults.

Omeprazole may be used short term or long term as prescribed by your doctor. OTC omeprazole is used short term.

As with other drugs, omeprazole can cause side effects (adverse effects). Read on to learn about potential common, mild, and serious side effects. For a general overview of omeprazole, including details about its uses, refer to this article. Your doctor can also tell you more about omeprazole.

Omeprazole can cause certain side effects, some of which are more common than others. These side effects may be temporary, lasting a few days to weeks. However, if the side effects last longer than that, bother you, or become severe, be sure to talk with your doctor or pharmacist.

These are just a few of the more common side effects reported by people who took omeprazole capsules or tablets in clinical trials:

  • headache
  • flatulence (gas)
  • mild diarrhea*
  • nausea and vomiting*
  • stomach pain or abdominal pain*

* For more information about this side effect, see the “Omeprazole: Side effect specifics” section below.

Mild side effects can occur with omeprazole use. This list doesn’t include all possible mild side effects of the drug. For more information, you can refer to the prescribing information for omeprazole capsules or tablets.

Mild side effects that have been reported with omeprazole include:

These side effects may be temporary, lasting a few days to weeks. However, if the side effects last longer than that, bother you, or become severe, be sure to talk with your doctor or pharmacist.

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks side effects of the medication. If you develop a side effect while taking omeprazole and want to tell the FDA about it, visit MedWatch.

* For more information about this side effect, see the “Omeprazole: Side effect specifics” section below.

Omeprazole may cause serious side effects. The list below may not include all possible serious side effects of the drug. For more information, you can refer to the prescribing information for omeprazole capsules or tablets.

If you develop serious side effects while taking omeprazole, call your doctor right away. If the side effects seem life threatening or you think you’re having a medical emergency, immediately call 911 or your local emergency number.

Serious side effects that have been reported and their symptoms include:

* For more information about this side effect, see the “Omeprazole: Side effect specifics” section below.
† An allergic reaction is possible after taking omeprazole. However, it’s not clear whether this side effect occurred in clinical trials of omeprazole capsules or tablets. To learn more, see the “Omeprazole: Side effect specifics” section below.

Omeprazole capsules are used in children to treat:

Side effects of omeprazole in children are generally similar to side effects in adults who take the drug. Examples of these side effects are described throughout this article.

However, in clinical trials of omeprazole capsules, upper respiratory infections such as the common cold occurred more often in children than in adults. Also, otitis media (middle ear infection) and fever were commonly reported in children.

If your child has been prescribed omeprazole and you’re concerned about side effects, talk with their doctor.

Note: Over-the-counter omeprazole tablets are not approved for use in children.

Over-the-counter omeprazole comes as delayed-release (DR)* tablets and capsules in a strength of 20 milligrams (mg). Prescription omeprazole comes as DR capsules in strengths of 10 mg, 20 mg, and 40 mg.

Omeprazole DR 40-mg can cause the same types of side effects as the other strengths. However, as with many drugs, taking a higher dosage of omeprazole may increase your risk of certain side effects.

For example, with a dosage† of omeprazole 40 mg twice daily, side effects are more likely than with a dosage of 20 mg once daily. Specifically, you may have an increased risk of bone fractures (breaks) and a low vitamin B12 level if you take a high dosage of omeprazole.

Your doctor will always prescribe the lowest possible omeprazole dosage for the shortest possible time to treat your condition. If you’re concerned about your dosage and any possible side effects, talk with your doctor.

* Delayed release means the active ingredient is not released until it passes through your stomach. This helps prevent the drug from being deactivated by the acid in your stomach.
† To learn about the dosages of omeprazole, see this article.

Certain side effects of omeprazole typically only develop if you take the drug for long periods of time. Long-term use of omeprazole can increase your risk of the following side effects:

If your doctor prescribes omeprazole for a long time, they may order blood tests to check your magnesium and vitamin B12 levels. If you develop low levels, your doctor will likely prescribe supplements to correct them. They may also recommend that you stop taking omeprazole.

If your doctor prescribes omeprazole for longer than a year, talk with them about your risk of bone fractures. They may recommend taking calcium and vitamin D supplements to help keep your bones strong and reduce your risk of fractures.

Omeprazole may cause several side effects. Here are some frequently asked questions about the drug’s side effects and their answers.

Is weight gain or weight loss a side effect of omeprazole?

Possibly. Weight changes weren’t reported in clinical trials of omeprazole capsules or tablets. However, certain side effects of omeprazole may cause weight changes.

For instance, if you have nausea* with omeprazole, this may reduce your appetite and lead to weight loss. And if you have severe diarrhea* with omeprazole, this could also lead to weight loss. Weight loss can also be a symptom of a low vitamin B12 level, which can occur with long-term use of omeprazole.

Weight gain has been reported in some people taking omeprazole since the drug was approved. However, it’s unclear how often this happened or whether omeprazole was the cause.

Since omeprazole treats conditions that cause digestive symptoms, you may have a reduced appetite. This could lead to weight loss. So if your condition improves with omeprazole treatment, your appetite may increase. This could lead to weight gain.

If you’re concerned about weight changes with omeprazole, talk with your doctor. They can investigate the possible cause and suggest ways to maintain a weight that is healthy for you.

* For details about nausea and diarrhea with omeprazole, see the “Omeprazole: Side effect specifics” section below.

Can omeprazole cause anxiety?

It’s possible. Anxiety wasn’t reported in clinical trials of omeprazole capsules or tablets. However, this side effect has been reported in some people taking omeprazole since the drug was approved. It’s unclear how often this has happened or whether omeprazole was the cause.

If you have anxiety with omeprazole, talk with your doctor. They can investigate possible causes and suggest ways to manage your condition.

Learn more about some of the side effects that omeprazole may cause. To find out how often side effects occurred in clinical trials, see the prescribing information for omeprazole capsules or tablets.

Constipation

Some people may have constipation while taking omeprazole. However, this side effect was rare in clinical trials of omeprazole capsules. It’s not clear whether this side effect occurred in clinical trials of omeprazole tablets.

Note that constipation could be a symptom of a low vitamin B12 level, which may be associated with long-term use of omeprazole.

What you can do

If you have constipation while taking omeprazole, it will typically get better in a few days or weeks. You can help ease constipation by:

  • drinking lots of water
  • eating plenty of fiber-rich foods
  • doing gentle exercise, such as walking

If you have constipation that’s bothersome or doesn’t get better, talk with your doctor. They may recommend taking a laxative medication or other measures to ease the problem. They may also order a blood test to check your vitamin B12 level.

Diarrhea

Diarrhea may occur during omeprazole treatment. Diarrhea was one of the more common side effects reported in clinical trials of omeprazole capsules. It’s not clear whether this side effect occurred in clinical trials of omeprazole tablets.

Diarrhea is typically mild. However, omeprazole can sometimes cause a bacterial infection due to Clostridium difficile (C. diff) bacteria in your intestines. This can result in severe watery diarrhea. It’s important to note that if you take omeprazole with antibiotics, you may have an increased risk of this type of diarrhea.

What you can do

If you have diarrhea while taking omeprazole, it will typically get better in a few days or weeks. It’s important to drink plenty of fluids to avoid getting dehydrated. If you’d like to take medications to treat diarrhea, be sure to talk with your doctor first.

Contact your doctor if you have diarrhea that’s severe or doesn’t go away. Also, contact them if you have other symptoms, such as a fever, or blood or pus in your stool. Your doctor may prescribe antibiotics or other treatments if you have diarrhea caused by a C. diff infection.

Nausea

Some people may have nausea while taking omeprazole. Nausea was one of the more common side effects reported in clinical trials of omeprazole capsules. It’s not clear whether this side effect occurred in clinical trials of omeprazole tablets.

Nausea is typically mild. However, nausea can also be a symptom of certain serious side effects that omeprazole may cause. This includes kidney problems. (To learn more, see the “Omeprazole: Serious side effects” section above.)

Nausea can also be a symptom of the conditions omeprazole is used to treat.

What you can do

If you have nausea while taking omeprazole, it will typically get better in a few days or weeks. It may help to take the medication with a meal or snack.

Here are some other tips for managing nausea:

  • eat small amounts frequently, rather than eating large main meals
  • avoid greasy, rich, or spicy foods
  • take frequent sips of water
  • get plenty of fresh air

If you have nausea that’s bothersome, severe, or doesn’t go away, talk with your doctor. They can try to determine its cause.

Stomach pain or abdominal pain

Stomach or abdominal pain may occur while taking omeprazole. This was among the more common side effects reported in clinical trials of omeprazole capsules. It’s not clear whether this side effect occurred in clinical trials of omeprazole tablets.

Stomach or abdominal pain may be related to other side effects of omeprazole, such as constipation, diarrhea, or gas. It can also be a symptom of the conditions omeprazole is used to treat.

What you can do

If you have stomach or abdominal pain while taking omeprazole, it will typically get better in a few days or weeks. It may help to:

  • place a hot water bottle on your abdomen
  • eat in small amounts frequently, rather than eating large main meals
  • lie down and rest

If you have stomach or abdominal pain that’s bothersome, severe, or doesn’t go away, talk with your doctor. They may want to investigate possible causes.

Allergic reaction

As with most drugs, omeprazole can cause an allergic reaction in some people. However, it’s not clear whether this side effect occurred in clinical trials of omeprazole capsules or tablets.

Symptoms can be mild or serious and can include:

  • skin rash
  • itching
  • flushing
  • swelling under your skin, typically in your eyelids, lips, hands, or feet
  • swelling of your mouth, tongue, or throat, which can make it hard to breathe

What you can do

For mild symptoms of an allergic reaction, call your doctor right away. They may recommend ways to ease your symptoms and determine whether you should keep taking omeprazole. However, if your symptoms are serious and you think you’re having a medical emergency, immediately call 911 or your local emergency number.

Be sure to talk with your doctor about your health history before you take omeprazole. This drug may not be the right treatment option for you if you have certain medical conditions or other factors that affect your health. These are known as drug-condition or drug-factor interactions. The conditions and factors to consider include:

Allergic reaction. In certain cases, your doctor will likely recommend that you do not take omeprazole. These include an allergic reaction to omeprazole, any of its ingredients, or other proton pump inhibitor drugs. (Omeprazole belongs to the proton pump inhibitor drug class.) Taking omeprazole could cause you to have another allergic reaction. Examples of other proton pump inhibitor drugs include esomeprazole (Nexium) and lansoprazole (Prevacid). Ask your doctor what other medications may be better options for you.

Osteoporosis. Taking omeprazole at a high dosage* or for longer than a year may raise your risk of bone fractures (breaks). If you already have weakened bones due to osteoporosis, you may have a higher risk of bone fractures with omeprazole. Talk with your doctor about whether omeprazole is safe for you.

Certain types of lupus. Omeprazole can cause and worsen cutaneous lupus erythematosus and systemic lupus erythematosus. If you have one of these conditions, talk with your doctor about whether omeprazole is safe for you.

Liver problems. Your liver is responsible for breaking down omeprazole. If you have liver problems, omeprazole could build up in your body and increase your risk of side effects. Due to this risk, your doctor may prescribe a low omeprazole dosage* if you have liver problems.

Asian descent. If you’re of Asian descent, your body may not break down omeprazole well. This could cause the drug to build up in your bodyand increase your risk of side effects. Due to this risk, your doctor may prescribe a low omeprazole dosage.* If you have questions about this, talk with your doctor.

Other medications. Be sure to tell your doctor or pharmacist about other drugs that you take.Omeprazole can interact† with certain other medications. These include rilpivirine (Edurant), clopidogrel (Plavix), rifampin (Rifadin, Rimactane), and the herbal supplement St. John’s wort. If you take one of these medications, your doctor will likely recommend that you do not take omeprazole. Talk with them about what other drugs may be better options for you.

* To learn about the dosages of omeprazole, see this article.
† For details about omeprazole interactions, view this article.

Alcohol with omeprazole

Alcohol hasn’t been reported to interact with omeprazole. However, drinking alcohol could worsen some of omeprazole’s side effects, such as nausea, diarrhea, and headache. It could also worsen symptoms of the condition you’re taking omeprazole to treat.

If you drink alcohol, talk with your doctor about how much, if any, is safe to consume while you’re taking omeprazole.

Pregnancy and breastfeeding while taking omeprazole

It’s not known whether omeprazole is safe to take during pregnancy. If you’re pregnant or plan to become pregnant, talk with your doctor about whether taking omeprazole is safe for you.

Omeprazole may pass into breast milk in small amounts. It’s not known whether this may cause side effects in a child who’s breastfed.

If you’re breastfeeding or plan to breastfeed, talk with your doctor about the best way to feed your child while taking omeprazole.

Side effects aren’t especially common with omeprazole. Most of the omeprazole’s side effects are mild and ease as your body gets used to the medication. However, some serious side effects are also possible, especially if you take the drug for a long period of time.

It’s important to note that if you take omeprazole to remove Heliobacter pylori bacteria from your digestive system, your doctor will likely prescribe it with antibiotics. Antibiotics may also cause side effects.

If you’d like to learn more about omeprazole, talk with your doctor or pharmacist. They can help answer any questions you have about side effects of taking the drug. Referring to the following articles about omeprazole can provide you with additional information:

  • More information about omeprazole. For details about other aspects of omeprazole, refer to this article.
  • Cost. If you’d like to learn about omeprazole and cost, see this article.
  • A look at your condition. For details about gastrointestinal problems, see our list of related articles.

Disclaimer: Medical News Today has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.