5 Supplements That Can Cause Diarrhea and How to Prevent It

A vitamin or mineral supplement is part of the typical wellness routine for many people. Certain supplements, however, can come with the side effect of diarrhea.

This is known as osmotic diarrhea. This type of diarrhea is most commonly associated with things we ingest, like certain supplements, says Caroline Renee Jouhourian, MD, a gastroenterology specialist in North Chelmsford, Massachusetts. The cause of the osmotic diarrhea prevents proper water and electrolyte absorption, according to Cleveland Clinic.

No matter the cause, having diarrhea is unpleasant at best, and there is always a risk of becoming dehydrated. Here are five supplements that can cause diarrhea and what you can do to prevent it.

1. Vitamin C

Vitamin C is a water-soluble nutrient, which means it can't be stored in the body for later use. Adults are recommended to get 75 milligrams (mg) to 90 mg per day, according to Mayo Clinic. Women who are pregnant or breastfeeding will need a higher amount.

The upper limit, or the maximum amount, you should have in any given day, is 2,000 mg. Megadoses of vitamin C can cause diarrhea as well as vomiting, cramps, nausea, and other symptoms. But it's rare to get that much vitamin C through diet alone, Dr. Jouhourian says.

2. Zinc

According to the National Institutes of Health Office of Dietary Supplements, zinc plays a role in immune cell function, normal physical development, and preventing inflammation. Adults should aim for 8 mg to 12 mg of zinc a day.

While zinc is found in almost all multivitamin supplements, most people get what they need from zinc-rich foods, including oysters, meat, fortified cereals, beans, nuts, whole grains, and some dairy products, according to the Office of Dietary Supplements.

Getting too much zinc can bring excess water into the intestine, contributing to diarrhea, Jouhourian says.

3. Fish Oil

Omega-3 fatty acids — found in fatty fish — are associated with heart health, reduced inflammation, and improved cognition, according to the Office of Dietary Supplements.

That said, people who take a fish oil supplement may experience "slippery" poop, Jouhourian says, and diarrhea in some cases. That's because fish oil contains a lot of fat, which essentially serves as a lubricant in the gastrointestinal tract.

"Fish oil is similar to a stool softener, but it doesn't necessarily soften it — it's like a slip and slide," she says, adding that if you take too much, it could lead to diarrhea.

Your system might get used to fish oil so you stop having episodes of diarrhea, but if you continue to experience loose, watery stools for more than a day or two, it's time to discuss alternative options with your healthcare professional, according to Mayo Clinic.

4. Magnesium

Magnesium is a crucial nutrient for protein synthesis, muscle and nerve function, and blood pressure regulation, according to the Office of Dietary Supplements. Magnesium is found in leafy green vegetables, legumes, nuts, seeds, and whole grains.

The recommended daily intake for adults is 310 mg to 420 mg, according to the Office of Dietary Supplements. Only about half of Americans get the amount they need daily from food alone.

"A lot of people might take magnesium for their immune system or cardiovascular health," Jouhourian says. And for those who have a cardiac arrhythmia and are taking magnesium, for example, diarrhea might be an issue, so their doctors might prescribe an antidiarrheal medication, she says.

Antacids with magnesium might also cause diarrhea, according to MedlinePlus.

5. Laxatives

This might go without saying: Laxatives are designed to cause diarrhea. Laxatives work by pulling water into the gut or causing the intestinal muscle to contract, according to Mayo Clinic.

There are times when doctors might recommend a laxative, Jouhourian says, for reasons like constipation relief.

"It's okay to take a laxative here and there," Jouhourian says. "But they shouldn't be taken every day and should be taken under the guidance of a doctor." What can be dangerous and never recommended, she says, is taking a laxative for weight loss.

Taking a laxative for weight loss can lead to severe health issues, according to the National Eating Disorders Association (NEDA):

• Electrolyte and mineral imbalances, which can cause organ dysfunction
• Severe dehydration, which can lead to kidney damage, tremors, weakness, fainting, and in some cases, death
• Laxative dependency, which happens when the colon stops reacting to recommended doses of laxatives and requires larger amounts to produce bowel movements
• Internal organ damage
• Increased risk of colon cancer

If you or someone you know is struggling with an eating disorder or disordered eating, help is available. The NEDA has resources available on its website.

Tips to Avoid Diarrhea From Supplements

If your supplement is sending you running for the bathroom, there are measures you can take to mitigate those effects.

1. Split Your Supplement Doses in Half

Spreading out your supplement dose can help ease any diarrhea you may be experiencing.

For example, you might try splitting your pill in half and taking half in the morning and half in the evening, Jouhourian says.

2. Take Your Supplement After Exercise

People who exercise are probably no stranger to the effects that movement can have on their gastrointestinal tract. Research has shown that strenuous exercise is sometimes linked with exercise-induced gastrointestinal syndrome.

"Exercise notoriously gets things going," Jouhourian says. She recommends taking a supplement after a workout and, perhaps more importantly, while eating, which can help settle the stomach.

3. Avoid Artificial Sweeteners

Regardless of whether you're taking a supplement that might cause diarrhea, fake sugars are osmotic stimulants that can lead to or worsen diarrhea, Jouhourian says. It's best to read labels and avoid polyols or sugar alcohols.

"The key with diarrhea is [avoiding] the culprit," she says.

4. Focus on Fiber

Fiber can be a little tricky, Jouhourian says. Eating the right amount — 14 grams for every 1,000 calories consumed, according to the Academy of Nutrition and Dietetics — will keep your gastrointestinal tract regular. But too much or too little fiber can lead to constipation or diarrhea.

In addition to eating enough fiber, make sure to stay hydrated. Jouhourian recommends drinking 64 ounces a day and more if you're physically active.