Quick answer

Potassium supplements can cause minor stomach and bowel side effects, NIH says, and the potassium chloride label lists diarrhea among the most common reactions to oral potassium salts. The potassium citrate label says the complaints may ease with meals. Ask your doctor if diarrhea or stomach pain persists.^1,2,3

Key facts

NIH says potassium supplements can cause minor gastrointestinal side effects.¹
The potassium chloride label lists nausea, vomiting, flatulence, abdominal pain and diarrhea as the most common reactions to oral potassium salts.²
The potassium citrate label says minor complaints may be eased by taking the dose with meals or snacks.³
NIH says diarrhea can lower the body's potassium through losses in the stool, which is the reverse direction.¹
Most potassium-only supplements hold 99 mg or less per serving, while FDA's rule on potassium salt medicines starts at 100 mg per tablet.^1,4

What does NIH say about potassium and the gut?

Potassium supplements can cause minor stomach and bowel side effects.¹

NIH says high dietary potassium does not pose a health risk to healthy people with normal kidney function, because the kidneys eliminate the excess in urine. The effects it lists come from supplements, salt substitutes and medicines that contain potassium salts.¹

What do prescription potassium labels list?

The prescription potassium chloride label says the most common adverse reactions to oral potassium salts are nausea, vomiting, flatulence, abdominal pain or discomfort and diarrhea. It adds that solid forms can produce ulcerative lesions in the gut if they stay in contact with the lining for long, that tablets should not be taken on an empty stomach, and that reports include obstruction, bleeding and perforation.²

The potassium citrate label lists minor gastrointestinal complaints such as abdominal discomfort, vomiting, diarrhea, loose bowel movements or nausea, and says they may be eased by taking the dose with meals or snacks or by reducing the dose.³

Why do many supplements stop at 99 mg?

Potassium salts in some oral medicines have been linked to small-bowel lesions that caused obstruction, bleeding and perforation. FDA rules for these medicines cover tablets with 100 mg or more of potassium, which is why many supplement makers stop at 99 mg. FDA has not ruled on whether supplements above 99 mg need a warning.^1,4

NIH says most potassium-only supplements hold up to 99 mg of potassium per serving. FDA's rule on potassium salt medicines starts at tablets supplying 100 mg or more of potassium.^1,4

What about constipation, and diarrhea going the other way?

NIH says mild low potassium is characterized by constipation, fatigue, muscle weakness and malaise. It also says low potassium is rarely caused by low dietary intake alone and can result from diarrhea, because potassium is lost in the stool.¹

So constipation or diarrhea can be linked to potassium in either direction. NIH notes that blood tests give only a rough picture of the body's potassium stores, because almost all of it sits inside cells, so ask your doctor rather than guess.¹

Who should ask a doctor about potassium and stomach problems?

Anyone with severe vomiting, stomach pain, bloating or bleeding while taking potassium, which the label says could mean ulceration or obstruction.²
Anyone with kidney disease or on an ACE inhibitor, ARB or diuretic.¹
Anyone with ongoing diarrhea or vomiting, which can change potassium levels.¹

Ask your doctor. The label treats severe vomiting, pain or bleeding as a reason to stop the drug and consider ulceration or obstruction.

Questions people ask

Does potassium cause constipation or diarrhea?

NIH says potassium supplements can cause minor stomach and bowel side effects, and the potassium chloride label lists diarrhea among the most common reactions. NIH also says low potassium can bring constipation.^1,2

Does potassium chloride cause diarrhea?

The prescription label lists nausea, vomiting, flatulence, abdominal pain and diarrhea as the most common reactions to oral potassium salts. Ask your doctor if they persist.²

Does potassium citrate cause diarrhea?

The label lists diarrhea and loose bowel movements among minor complaints, which it says may be eased by taking the dose with meals or snacks. Ask your doctor.³

Does low potassium cause constipation?

NIH says mild low potassium is characterized by constipation, fatigue and muscle weakness, and that diarrhea can itself lower potassium through losses in the stool. Ask your doctor.¹

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Sources

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.