Medications are a primary or contributing cause of high potassium in 35% to 75% of hospitalized patients, and older adults face the highest risk. The most common culprits are blood pressure drugs that affect the renin-angiotensin-aldosterone system, but several other widely prescribed medications can push potassium to dangerous levels, especially when kidney function has declined with age.
Normal blood potassium falls below 5.0 mmol/L. Mild hyperkalemia starts at 5.5, moderate at 6.0, and severe (which can trigger cardiac arrest) at 6.5 mmol/L or above. Many of the drugs on this list are essential medications, so the goal isn’t to avoid them but to understand why monitoring matters.
ACE Inhibitors and ARBs
These are the single most common drug cause of high potassium. ACE inhibitors (lisinopril, enalapril, captopril) and ARBs (losartan, candesartan) lower blood pressure by blocking the hormone system that also tells your kidneys to release potassium. When that system is suppressed, your kidneys hold on to more potassium than they normally would. ACE inhibitors alone account for about 25% of all drug-suspected hyperkalemia cases.
Millions of older adults take these drugs for high blood pressure, heart failure, or kidney protection in diabetes. They work well and have real benefits. The risk rises when kidney function is already reduced, which is common in people over 65 even without a kidney disease diagnosis. Current guidelines recommend checking potassium within one week of starting one of these drugs or increasing the dose, with more frequent checks for anyone who also has chronic kidney disease, diabetes, or heart failure.
Potassium-Sparing Diuretics
Spironolactone and eplerenone block aldosterone, the hormone that signals your kidneys to flush potassium out. Without that signal, potassium accumulates. Spironolactone is prescribed frequently for heart failure and resistant high blood pressure, and it accounted for about 9% of drug-related hyperkalemia reports in one national safety review.
Two other potassium-sparing diuretics, amiloride and triamterene, work through a slightly different mechanism but produce the same result: they block the channels in the kidney that allow potassium to leave the body. Triamterene is often bundled with hydrochlorothiazide in a single pill, so some people take it without realizing they’re on a potassium-sparing drug. If you’re on any of these, potassium supplements or salt substitutes (which contain potassium chloride) can compound the problem quickly.
NSAIDs: A Common Over-the-Counter Risk
Ibuprofen, naproxen, diclofenac, and meloxicam all reduce potassium excretion by suppressing aldosterone production through a different pathway than ACE inhibitors. Many older adults take these regularly for arthritis or chronic pain, and they’re available without a prescription, which makes them easy to overlook during medication reviews.
The risk is particularly high when NSAIDs are combined with an ACE inhibitor or spironolactone, because both drugs are now working to keep potassium in the body through complementary mechanisms. Even short courses of NSAIDs can tip potassium levels in someone whose kidneys are already working at reduced capacity.
Trimethoprim: The Antibiotic Surprise
Trimethoprim, most commonly prescribed as part of the combination antibiotic trimethoprim-sulfamethoxazole (Bactrim), is one of the most underappreciated causes of high potassium in older adults. Its chemical structure resembles the potassium-sparing diuretic amiloride, and it reduces the kidneys’ ability to excrete potassium by roughly 40%.
This becomes dangerous when an older patient already taking spironolactone gets a prescription for Bactrim to treat a urinary tract infection. A large study published in The BMJ found that this combination increased the risk of hospitalization for hyperkalemia by more than 12 times compared to patients given amoxicillin instead. The researchers estimated that about 60% of all hyperkalemia cases in older spironolactone users treated with an antibiotic for a UTI could be prevented simply by choosing a different antibiotic. Despite this, roughly 11% of spironolactone users in the study received at least one Bactrim prescription. The combination of trimethoprim-sulfamethoxazole with ACE inhibitors or ARBs has also been linked to an increased risk of sudden death.
Beta-Blockers
Beta-blockers like metoprolol, atenolol, bisoprolol, and propranolol are staples for managing high blood pressure, heart failure, and irregular heart rhythms. They raise potassium through a subtler mechanism than the drugs above. Normally, your body’s stress-response hormones (adrenaline and related chemicals) help push potassium from the bloodstream into cells. Beta-blockers dampen that process, leaving more potassium circulating in the blood.
On their own, beta-blockers rarely cause severe hyperkalemia. The real concern is the additive effect: an older adult taking a beta-blocker alongside an ACE inhibitor and spironolactone for heart failure is now on three drugs that all raise potassium through different pathways.
Heparin and Blood Thinners
Heparin and low-molecular-weight versions like enoxaparin are potent suppressors of aldosterone production in the adrenal glands. This effect kicks in within a few days of starting treatment, is reversible when the drug is stopped, and can occur at relatively low doses. Prolonged use actually shrinks the part of the adrenal gland responsible for making aldosterone.
This is most relevant for older adults hospitalized for blood clots or those receiving heparin injections to prevent clots after surgery. The potassium rise is usually modest, but it adds risk for patients already on other potassium-raising medications.
Other Medications That Raise Potassium
Several less commonly discussed drugs also contribute:
- Digoxin, used for heart failure and atrial fibrillation, impairs the cellular pump that moves potassium into cells. Toxicity from digoxin can cause dangerous potassium spikes.
- Potassium supplements themselves are an obvious but frequently overlooked source. Older adults sometimes continue taking prescribed potassium chloride even after starting a potassium-sparing drug.
- Immunosuppressive drugs like cyclosporine and tacrolimus, used after organ transplants, reduce potassium excretion through the kidneys.
- Lithium, a mood stabilizer, can also raise potassium levels, though the mechanism isn’t fully understood.
Why Older Adults Are Especially Vulnerable
Aging kidneys filter blood less efficiently, even in otherwise healthy people. By age 70, most adults have lost a meaningful portion of their kidney filtration capacity compared to age 30. This means the kidneys’ ability to dump excess potassium is already compromised before any medication enters the picture. Diabetes and chronic kidney disease, both common in older adults, reduce potassium excretion further.
Older adults also tend to take more medications simultaneously. A typical scenario involves someone on lisinopril for blood pressure, spironolactone for heart failure, and then prescribed Bactrim for a urinary tract infection. Each drug independently raises potassium, and together they can push levels into a dangerous range within days. Adding an over-the-counter NSAID for back pain makes the situation worse.
What Monitoring Looks Like
Potassium levels are checked with a simple blood draw. If you’re starting or increasing the dose of an ACE inhibitor, ARB, or potassium-sparing diuretic, expect a blood test within the first week or two. After that, the frequency depends on your individual risk. People with kidney disease, diabetes, heart failure, or a history of high potassium readings typically need more frequent checks, sometimes every few months.
Symptoms of high potassium can be subtle or absent until levels become dangerous. When they do appear, they include muscle weakness, tingling or numbness, nausea, and an irregular or slow heartbeat. Because symptoms are unreliable, routine blood testing is the only way to catch rising levels early. If you’re on multiple medications from the categories above, make sure every prescriber knows your full medication list, including over-the-counter drugs like ibuprofen and any potassium supplements or salt substitutes you use at home.