Quick answer

For healthy adults with normal kidney function, potassium from food has not been shown to cause harm, and supplements of 99 mg or less add little. Supplements can cause minor stomach and bowel upset. Several common medicines and some health problems make extra potassium risky, so ask a pharmacist before adding any.^1,2

Key facts

No tolerable upper intake level is set for potassium in healthy people.²
Salt substitutes can hold 440 to 2,800 mg of potassium per teaspoon, many times a supplement.²
In healthy people, very large supplement amounts can exceed what the kidneys clear.²
Potassium leaves the body mainly in urine, so the kidneys set how much the body can handle.²

Side effects reported

Potassium supplements can cause minor stomach and bowel side effects.²

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.^2,3

The prescription potassium chloride label tells people to stop the tablets and get medical help for severe vomiting, abdominal pain, swelling of the abdomen or bleeding from the gut, and to report black, tarry stools.⁴

When potassium gets too high

Too much potassium in the blood (hyperkalemia) can cause muscle weakness, paralysis, heart palpitations, a burning or prickling feeling in the hands and feet, and irregular heart rhythms that can be life threatening. It can also cause no symptoms until it is severe.²

Very large amounts of potassium from supplements or salt substitutes can exceed what the kidneys can clear and cause hyperkalemia even in healthy people. In people with kidney disease or on certain medicines, it can happen even at ordinary food intakes.^1,2

Because high potassium can go unnoticed until it is severe, NIH says experts recommend checking potassium in people who take ACE inhibitors, ARBs or potassium-sparing diuretics, especially if their kidneys are not working well.²

Who should not add potassium without a doctor

People with kidney disease or reduced kidney function²
People with type 1 diabetes, heart failure, liver disease or adrenal insufficiency, in whom NIH says high blood potassium can also develop^1,2
People taking an ACE inhibitor, an ARB or a potassium-sparing diuretic¹
People taking NSAID pain relievers regularly, which the potassium chloride label says can make the body keep potassium⁴

Avoid the combination unless your doctor advises it

The spironolactone label says potassium supplements taken with it may lead to severe hyperkalemia, and that patients should be advised to avoid potassium supplements and foods high in potassium, including salt substitutes.^5,6

On the medicine's label

Older adults

The potassium chloride label advises cautious dosing in older people, usually starting at the low end, because they more often have reduced kidney, liver or heart function and take other medicines. The drug is cleared mainly by the kidneys, so poorer kidney function raises the chance of toxic effects.⁴

People with diabetes

NIH lists type 1 diabetes among the conditions in which blood potassium can climb too high, and the lisinopril label names diabetes as a risk factor for high potassium during treatment. ACE inhibitors and ARBs, which raise potassium, are also prescribed to slow kidney disease in people with type 2 diabetes. Ask your doctor before any potassium supplement or salt substitute.^2,7

Food compared with supplements

Potassium in food and drink has not been shown to harm healthy people with normal kidney function, because the kidneys pass the excess in urine. Healthy kidneys respond quickly, stepping up excretion soon after potassium comes in. The concern is concentrated sources and anything that limits what the kidneys can pass.^1,2

Questions people ask

Can potassium supplements upset your stomach?

Yes. Minor stomach and bowel side effects are the usual complaint, NIH says, and the prescription potassium chloride label pairs each dose with a meal and a full glass of liquid partly to protect the gut.^2,4

What are the signs of too much potassium?

Muscle weakness, paralysis, heart palpitations, a burning or prickling feeling in the hands and feet, and irregular heart rhythms. High potassium can also cause no symptoms at all, so it is found with a blood test.²

Is a salt substitute safer than a supplement?

Not necessarily: salt substitutes can hold far more potassium, 440 to 2,800 mg per teaspoon. The labels for lisinopril, losartan and spironolactone all tell people to check with their doctor before using them, or to avoid them.^2,5,7,8

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Sources

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