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A cup of fish oil pills.
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Fish oil, a supplement rich in omega-3 fatty acids frequently touted for its protective effects on the heart, isn't right for everyone. In fact, fish oil may cause negative side effects particularly when used by people with diabetes -- a condition characterized by unusually high blood sugar levels. If you have diabetes, be sure to talk with your primary care provider before beginning treatment with fish oil supplements.

Elevated Blood Sugar

The omega-3 fatty acids present in fish oil may raise your blood sugar level. An increase in blood sugar levels can be particularly harmful for people who already have diabetes. If your diabetes is controlled by medication, you may begin to experience diabetes symptoms again while taking fish oil supplements. Such symptoms include increased urination and thirst, sudden weight loss, fatigue and blurred vision. Seek prompt care from your doctor if you develop any of these symptoms, especially if you have already been diagnosed with diabetes. Uncontrolled blood sugar levels may cause severe and permanent kidney and nerve damage.

Diabetes Drug Interaction

Always discuss all medications you are currently taking with your primary medical provider before beginning treatment with dietary or herbal supplements, including fish oil. The blood sugar raising effects of fish oil may reduce the efficacy of any diabetes medications you are currently taking, including glipizide, metformin, glyburide or insulin, the University of Maryland Medical Center warns. Consequently, your doctor may need to increase the amount of diabetes medication you take each day to counteract the blood sugar effects of fish oil.

Additional Side Effects

People with diabetes may also experience side effects that are common among most people during treatment with fish oil supplements. Omega-3 fatty acids may irritate your digestive tract, leading to frequent belching, excess gas, heartburn and loose stools. Your breath may also give off an embarrassing fishy odor despite your excellent oral hygiene. Taking more than 3 g of fish oil daily, which is not advised unless you're under the care of a doctor, may also increase your risk of experiencing bleeding complications. Such complications may include easy bruising or nose bleeds. In most instances, these side effects are mild; however, if you experience severe side effects, such as sharp stomach pain or chronic diarrhea, be sure to seek additional care from your physician.

Additional Drug Interactions

If you have diabetes, you may also have high blood pressure, also called hypertension. Concomitant use of fish oil supplements and antihypertensive drugs, including hydrochlorothiazide, furosemide, valsartan and enalapril, may reduce the efficacy of these prescription medications, MedlinePlus reports. Taking these medications together may cause a sudden drop in blood pressure and may cause dizziness, fatigue or headache.

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