If you’re taking an omega-3 supplement, you should know that you shouldn’t mix it with some prescription medications or even over-the-counter vitamins. Taking these supplements and meds at the same time can change how they work or even be unsafe.

1. Blood Thinners

Blood-thinning medications, such as warfarin, can interact with many other drugs and supplements, including omega-3s.

Some studies suggest that fish oil supplements may affect how blood clots. Taking them alongside a blood thinner could increase your risk of bleeding, which can be dangerous.

However, other research has found no major issues with the combination. People with heart conditions should talk to their healthcare provider, who can help determine whether the benefits of fish oil outweigh the potential risks when used with a blood thinner.

2. Blood Pressure Meds or Supplements

Prescription drugs and supplements used to lower blood pressure may not be safe to combine with omega-3 supplements, since all of them can reduce blood pressure.

Older studies suggested that taking fish oil along with blood pressure medication could cause blood pressure to drop too low. As with blood-thinning drugs, healthcare providers should weigh the risks and benefits of fish oil supplements for people taking heart medications.

3. Birth Control Pills

If you take birth control pills, be cautious about using omega-3 supplements to lower triglyceride levels. Some older studies suggested that birth control pills may reduce the effectiveness of fish oil in lowering triglycerides.

However, there’s no evidence that fish oil affects how well birth control pills prevent pregnancy.

4. Orilstat

Orlistat, available by prescription and over-the-counter, supports weight loss but can interfere with omega-3 supplements by affecting how your body absorbs fat.

Because fat is necessary for the body to absorb fish oil, taking orlistat may reduce the supplement’s effectiveness. To minimize this effect, take your fish oil supplement at least two hours before or after your orlistat dose.

5. Vitamin E

Vitamin E is a fat-soluble antioxidant that helps protect cells from damage, supports the immune system, and promotes healthy skin. You can get it from foods like fruits, whole grains, and nuts, or from supplements.

Some studies suggest that fish oil may lower vitamin E levels, though it’s unclear why. More recent human studies indicate the two supplements can work well together.

If you’re unsure whether fish oil is safe to take with your medications or other supplements, talk with your healthcare provider or pharmacist.