Omeprazole, one of the most widely used heartburn and acid reflux medications, is generally well tolerated, but it does carry a range of side effects from mild to serious. The most common ones, like headache and diarrhea, affect roughly 1 to 14 percent of users. Long-term use introduces additional risks involving bone health, nutrient absorption, and kidney function that are worth understanding if you’ve been on this medication for months or years.
Common Side Effects
The side effects most people experience are digestive. Diarrhea is the most frequent, occurring in up to 14% of users in clinical trials. Abdominal pain and nausea each affect between 1% and 10% of people. Headache falls in that same range and is the most commonly reported non-digestive side effect.
These tend to be mild and often resolve on their own as your body adjusts. If diarrhea or stomach pain persists beyond the first week or two, it’s worth flagging to your doctor, since these symptoms can occasionally signal something more than a routine side effect.
Bone Fracture Risk With Long-Term Use
Using omeprazole for longer than a year, especially at high doses, is associated with a modest increase in the risk of hip, wrist, and spine fractures. Two large meta-analyses found the risk rises by 10 to 40% above baseline. That sounds alarming, but context matters: if your baseline fracture risk is low, a 10 to 40% relative increase still translates to a small absolute risk. If you already have osteoporosis or other fracture risk factors, though, this becomes more clinically meaningful.
The mechanism isn’t entirely settled, but reducing stomach acid likely impairs calcium absorption over time. The UK’s medicines safety agency specifically flagged this concern for people on long-term, high-dose therapy.
Vitamin B12 and Magnesium Deficiency
Your stomach needs acid to extract vitamin B12 from food. By suppressing that acid, omeprazole can gradually reduce your body’s ability to absorb B12. Studies have found that taking the medication daily for a year or more increases the risk of B12 deficiency. Symptoms of low B12 include fatigue, numbness or tingling in your hands and feet, difficulty with balance, and memory problems. These develop slowly, so they’re easy to miss or attribute to other causes.
Low magnesium is another recognized risk with prolonged use. Symptoms include muscle cramps, tremors, irregular heartbeat, and seizures in severe cases. If you’ve been on omeprazole for over a year, periodic blood work to check these levels is a reasonable precaution.
Gut Infections
Stomach acid serves as a natural barrier against harmful bacteria. When you suppress it, certain infections become more likely. The one that gets the most clinical attention is C. difficile, a bacterial infection that causes severe, persistent diarrhea and can be difficult to treat.
A meta-analysis of 16 studies involving over 7,700 patients with C. difficile found that those on acid-suppressing medications had a recurrence rate of 22.1%, compared to 17.3% in patients not taking these drugs. That’s a meaningful difference if you’re already vulnerable to gut infections, particularly older adults or people who’ve recently taken antibiotics.
Kidney Problems
The FDA label for omeprazole includes a warning about a kidney condition called acute interstitial nephritis, a type of inflammation that can develop at any point during treatment. It’s considered rare but serious. Warning signs include a noticeable decrease in how much you urinate or blood in your urine. This reaction is thought to be an unpredictable immune response rather than something dose-related, meaning it can’t easily be prevented by taking a lower dose.
If it develops, the standard approach is to stop the medication. The condition is generally reversible when caught early.
Interaction With Blood Thinners
Omeprazole has a well-known interaction with clopidogrel, a blood-thinning drug commonly prescribed after heart attacks or stent placement. Both medications are processed by the same liver enzyme, and omeprazole can compete with clopidogrel for access to it. This theoretically reduces clopidogrel’s effectiveness at preventing blood clots.
However, a large recent study published in an American Heart Association journal found no significant difference in major cardiovascular events between patients taking clopidogrel with omeprazole versus those taking it with other acid reducers that don’t share this interaction. The event rates were nearly identical: 17.63 per 1,000 person-years versus 16.82. Still, many cardiologists prefer to use a different acid reducer in patients on clopidogrel, simply to avoid the theoretical concern.
Rare but Recognized Reactions
A small number of people develop a skin condition called subacute cutaneous lupus erythematosus while on omeprazole. It shows up as scaly, red patches on the skin, sometimes with joint pain. A Swedish study estimated the risk was about three times higher in people taking PPIs compared to the general population. While “three times higher” sounds significant, the baseline rate is very low, making this an uncommon reaction overall. It typically resolves after stopping the medication.
Side Effects in Children
Omeprazole is sometimes prescribed to infants and children with severe reflux. Based on adverse event reports submitted to the FDA, the most common side effects in this age group are vomiting (8.8% of reports), diarrhea (5.2%), excessive hair growth (4.1%), choking episodes (3.9%), and skin redness (3.7%). Cardiopulmonary events, including episodes of paused breathing, were reported in 7.8% of all pediatric cases, and C. difficile infection appeared in 1.3%.
Research has also linked long-term PPI use in children to increased rates of severe infections, including lower respiratory tract and gastrointestinal infections. These findings come primarily from adverse event databases rather than controlled trials, so the true risk is hard to pin down, but they reinforce that PPIs in children should be used at the lowest effective dose for the shortest necessary time.
What Happens When You Stop
Stopping omeprazole after regular use can trigger what’s called rebound acid secretion. While you’ve been on the medication, your body has been ramping up production of gastrin, the hormone that tells your stomach to make acid. When you remove the drug, all that extra gastrin suddenly has free rein, and your stomach produces more acid than it did before you started treatment.
One study found that more than 40% of previously symptom-free patients developed heartburn or indigestion within one week of stopping a four-week course. This rebound effect typically normalizes within two weeks. Tapering the dose gradually rather than stopping abruptly can help ease the transition, though not everyone needs to taper if they’ve only been on a short course.
This rebound effect is one reason people feel “stuck” on omeprazole. The returning symptoms can feel worse than the original problem, which leads to restarting the medication. If you’re trying to come off it, expect some temporary discomfort and consider stepping down to a lower dose or switching to an as-needed antacid during the transition period.