Common Side Effects
Omeprazole has been studied thoroughly in clinical trials. In these studies, the side effects that occurred in a group of people taking the drug were documented and then compared to the side effects that occurred in another group of people taking a placebo (a "sugar pill" that does not contain any active ingredients). As a result, it was possible to see what side effects occurred, how often they appeared, and how they compared to the group not taking the medicine.
In these studies, the most common omeprazole side effects included:
- Headaches -- in up to 6.9 percent of people
- Abdominal pain (or stomach pain) -- up to 5.2 percent
- Diarrhea -- up to 3.7 percent
- Upper respiratory tract infections, such as the common cold -- up to 1.9 percent
- Dizziness -- up to 1.5 percent
- Constipation -- up to 1.1 percent
- Back pain -- up to 1.1 percent.
Rare Omeprazole Side Effects
Rare side effects of omeprazole occur in less than 1 percent of people taking the drug. Because these side effects are so uncommon, it can be difficult to tell whether they are actually caused by omeprazole or by factors unrelated to the medication.
Some of these rare side effects include, but are not limited to: