Taking supplements might seem like a smart way to boost your health—but some can wreak havoc on your digestive system. While vitamins, herbs, and over-the-counter pills are often marketed as "natural" or"gut-friendly," doctors say certain supplements can actually cause nausea, bloating, constipation, or even long-term damage to your GI tract.

In fact, several commonly used supplements can irritate the stomach lining, disrupt digestion, or interact negatively with medications, especially if taken in high doses or for prolonged periods. To protect your gut and make more informed choices, here are the top supplements doctors say you may want to avoid—or take with caution—if you're concerned about your digestive health.

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1. Iron New Africa / Shutterstock

Iron is an essential mineral that’s crucial for healthy growth and aids in the production of hemoglobin, a protein found in red blood cells that helps transport oxygen throughout your body. Many people take iron supplements to prevent or treat deficiencies.

However, iron supplements can sometimes cause constipation, nausea, and stomach pain—especially when taken at doses over 45 mg per day, says Raj Dasgupta, MD, an ABIM Quadruple board-certified physician specializing in internal medicine, pulmonology, critical care, sleep medicine, and a medical reviewer for the National Council on Aging (NCOA).

Ferrous sulfate, a type of iron supplement commonly used to treat anemia, is the most likely to cause digestive issues, Dr. Dasgupta says, so talk to your doctor if you have any concerns.

2. Calcium

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Calcium is crucial in helping you build and maintain strong bones, muscles, and nerves. If you're deficient in calcium, your doctor may recommend taking both calcium and vitamin D supplements to boost your levels and help with absorption.

However, Dr. Dasgupta says that some calcium supplements can also lead to constipation and bloating, particularly at doses above 1,200 mg per day.

"Calcium carbonate is more likely to cause discomfort than calcium citrate," he says. So, check which one you're taking and speak to your doctor about alternatives if you're experiencing any GI issues.

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3. Magnesium iStock

Magnesium is a nutrient that the body needs to regulate muscle and nerve function, maintain blood sugar levels and blood pressure, and build protein, bones, and DNA. Many people also use magnesium supplements as a sleep aid.

However, "doses over 350 mg per day often cause diarrhea,” says Dr. Dasgupta. "Magnesium oxide and citrate forms are more likely to cause digestive upset."

If this happens to you, let your doctor know.

4. Fish oil or omega-3 supplements

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Fish oil or omega-3 supplements are some of the most popular on the market. They aid in a range of healthy functions from improving muscle activity and brain health to encouraging cell growth.

That said, Dr. Dasgupta warns these supplements “at doses above three grams per day can cause stomach discomfort, acid reflux, and diarrhea."

To reduce potential side effects, he suggests taking them with food.

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5. Vitamin C iStock

Vitamin C can boost your immune system and help your body heal faster. It can also help protect your cells against free radicals—an atom, molecule, or ion that damages cells and increases your risk of heart disease, cancer, and other diseases.

That said, Dr. Dasgupta warns that there is such a thing as too much vitamin C.

“High doses over 2,000 milligrams per day can lead to diarrhea, stomach cramps, and bloating due to vitamin C's acidity and water-attracting effect on the intestines,” he says. Make sure you're supplementing within a healthy range.

6. Probiotics

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In general, probiotics can be great for your overall gut health, helping to promote a diverse and balanced microbiota.

However, these supplements can also cause “gas, bloating, and stomach pain, especially in those with sensitive digestion," says Dasgupta. He suggests not going above 10 billion CFUs per day.

RELATED: The 5 Best Anti-Aging Probiotics

7. Protein powders Shutterstock

Protein powders can help you grow muscle, repair tissue, and produce important hormones. However, Dr. Dasgupta says you may experience one especially unpleasant downside by taking them—especially if you choose formulas made with whey or casein.

“Protein powders can lead to bloating, gas, and diarrhea, particularly for those who are lactose intolerant or consume more than 40 grams per serving," he says. To find the best formula that meets your needs and will keep your GI tract happy, check out our sister site's guide to the best protein powders, according to nutritionists.

8. Fiber

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Fiber supplements, including those made from psylliumhusk or inulin, can aid digestion by bulking up your stool and making it easier to pass. Fiber can also help you feel fuller for longer, which can help you overcome cravings and even lose weight.

However, Dr. Dasgupta says fiber supplements can also cause gas, bloating, and cramps if taken in high doses of over five grams per day. Take yours with plenty of water and make sure you're within healthy levels.

RELATED: 5 Fiber Deficiency Symptoms, According to Doctors

9. Zinc iStock

Zinc supplements can help improve your immune system, speed up the healing process when you’re wounded, and enhance your metabolism.

However, taking over 40 milligrams of zinc per day has been linked to nausea, diarrhea, and painful stomach cramps. Tell your doctor if you're experiencing these side effects.

10. Fat-soluble vitamins A, D, E, and K Shutterstock

Finally, fat-soluble vitamins like vitamins A, D, E, and K are important for your immune system, vision, blood clotting, and bone health.

However, they can be difficult to digest and absorb—especially when you take them on an empty stomach. To avoid unpleasant digestive symptoms, try eating fat-rich food before you take them.

Most importantly, whenever it comes to adding supplements into your daily routine, make sure you chat with your doctor first to confirm they're right for you, you know the correct dosage, and they won't interact with any other medications you're taking.