Side Effects of Potassium

Potassium sounds like a harmless “electrolyte”, but in concentrated forms it can be dangerous. The editorial team explains which side effects potassium drugs and supplements have, why hyperkalemia poses a threat to the heart, and who is in the zone of increased risk.

Why potassium requires caution

In people with healthy kidneys, potassium from food practically never causes problems: the kidneys quickly excrete the excess, and the intake from food is spread out over time. It is a different matter with concentrated drugs and supplements, which deliver a large dose all at once, as well as situations in which the kidneys cannot cope with excretion.

The main feature of potassium is that there is very little of it in the blood plasma, and the range of normal values is narrow — usually about 3.5–5.0 mmol/L. The heart is extremely sensitive to changes in this range. That is why the side effects of potassium fall into two very different groups: local ones, associated with irritation of the digestive tract, and systemic ones, associated with a rise in the potassium level in the blood.

In its 2019 report, the US National Academies did not establish a tolerable upper intake level of potassium for healthy people from food, but separately emphasized the risks of potassium supplements for people with reduced kidney function and against the background of certain medications. It is precisely these risk groups that determine the real danger.

In this article, the editorial team systematizes the known side effects of potassium drugs and supplements, explains who is at risk, and which symptoms are a reason to seek medical help immediately.

Side effects on the digestive tract

The most common adverse reactions to oral potassium drugs are nausea, vomiting, abdominal discomfort, flatulence, and diarrhea. Potassium salts, especially the chloride, have an irritant effect on the mucous membrane. Solutions and effervescent forms have a pronounced unpleasant salty-bitter taste, which also reduces tolerability.

A more serious risk is associated with potassium chloride tablets. Historically, enteric-coated tablets were associated with ulcers and strictures of the small intestine, because they released highly concentrated potassium in one place. Modern extended-release forms (a wax matrix, microencapsulated granules) have reduced this risk but not eliminated it completely. The instructions for such drugs warn about the possibility of damage to the esophagus and gastrointestinal tract.

The risk of local damage increases if the tablet is swallowed without enough water, taken while lying down, and also in people with slowed passage of food through the esophagus or intestine. This is precisely why the instructions for prescription potassium drugs usually indicate taking them during or after a meal, washed down with a glass of water.

• mild symptoms: nausea, belching, bloating, loose stools;
• alarming symptoms: chest pain when swallowing, severe abdominal pain, vomiting blood, black stools;
• alarming symptoms require stopping the intake and seeing a doctor.

Hyperkalemia: the main danger

Hyperkalemia is a rise in the concentration of potassium in the plasma above the upper limit of normal. Its danger lies in the fact that for a long time it may give no noticeable symptoms and then manifest as a dangerous disturbance of the heart rhythm. Weiner and Wingo (1998) not without reason called hyperkalemia “a potentially silent killer”.

When symptoms do appear, they are nonspecific: muscle weakness, tingling and numbness in the limbs, a feeling of “wobbly” legs, nausea, palpitations, or irregularities in the heart’s work. On the electrocardiogram, characteristic changes arise — peaked T waves, widening of the QRS complex, and in severe cases dangerous arrhythmias up to cardiac arrest (Palmer, Clegg, 2016).

In a healthy person with normal kidney function, reaching hyperkalemia through food alone is practically impossible. However, combining potassium supplements with certain drugs, dehydration, or hidden kidney disease can sharply change the situation. Concentrated liquid forms and self-directed dose increases are especially dangerous.

We will separately mention “pseudohyperkalemia” — a falsely high test result due to hemolysis of the sample, prolonged compression of the arm with a tourniquet, or active clenching of the fist during blood collection. That is why an unexpectedly high reading is usually rechecked.

Who is at risk

The main risk factor is reduced kidney function. In chronic kidney disease, the ability to excrete potassium falls, and even a moderate supplement can lead to its accumulation. The KDIGO clinical guidelines (2024) on chronic kidney disease separately address potassium control as part of managing such patients.

The second factor is medications. The review by Ben Salem et al. (2014) describes a wide list of drugs that raise the potassium level. The most important of them are listed in the table.

The risk group also includes people with diabetes mellitus (especially with kidney damage), heart failure, adrenal insufficiency, as well as elderly people, in whom kidney function declines with age even without a diagnosed disease.

Athletes form a separate situation: regular use of NSAIDs “for joint pain”, dehydration after training in the heat, and simultaneous use of several electrolyte products — this is a combination that can imperceptibly raise the risk.

How to reduce the risks

The first and most important rule is not to use high-dose potassium drugs without a laboratory-confirmed need and a doctor’s recommendation. For most people, dietary sources are sufficient. Supplements with a small potassium content as part of multivitamins or electrolyte drinks carry practically no risk for a healthy person.

The second rule is to take medications into account. If you take blood pressure drugs, diuretics, or regularly use anti-inflammatory agents, any potassium supplement, including salt substitutes based on potassium chloride, should be discussed with a doctor.

The third is to monitor symptoms and not ignore them. Muscle weakness, unusual tingling, and irregularities in the heart’s work while taking potassium require immediate assessment by a doctor and, as a rule, a blood test and ECG.

The fourth is to take the drug itself correctly: with food, with a glass of water, in an upright position, without chewing extended-release tablets. These simple steps significantly reduce the risk of damage to the digestive tract.

Editorial Conclusions

The side effects of potassium fall into local ones — irritation and, rarely, damage to the digestive tract — and systemic ones, the main of which is hyperkalemia. It is precisely hyperkalemia that poses a real threat to life through its effect on the heart rhythm.

For a healthy person, potassium from food does no harm. The risk rises sharply in kidney diseases, when taking drugs that retain potassium, in dehydration, and with self-directed use of concentrated forms.

The editorial team advises regarding potassium drugs as medicines rather than as “safe electrolytes”, and taking them only after tests and a consultation with a doctor.

We also advise familiarizing yourself with our articles “Who Should Not Take Potassium”, “Potassium: Available Forms and Which to Choose”, and the piece on blood electrolyte tests.

References

1. Palmer BF, Clegg DJ. Physiology and pathophysiology of potassium homeostasis. Adv Physiol Educ. 2016;40(4):480–490.
2. Weiner ID, Wingo CS. Hyperkalemia: a potential silent killer. J Am Soc Nephrol. 1998;9(8):1535–1543.
3. Ben Salem C, Badreddine A, Fathallah N, Slim R, Hmouda H. Drug-induced hyperkalemia. Drug Saf. 2014;37(9):677–692.
4. Gumz ML, Rabinowitz L, Wingo CS. An integrated view of potassium homeostasis. N Engl J Med. 2015;373(1):60–72.
5. Kidney Disease: Improving Global Outcomes (KDIGO) CKD Work Group. KDIGO 2024 clinical practice guideline for the evaluation and management of chronic kidney disease. Kidney Int. 2024;105(4S):S117–S314.
6. National Academies of Sciences, Engineering, and Medicine. Dietary Reference Intakes for Sodium and Potassium. Washington, DC: National Academies Press; 2019.