Nursing care
Why do ACE inhibitors cause hyperkalemia? The aldosterone link explained
Written and reviewed by Nicole Ramirez, BSN, RN, CMSRN · 4 min read · Updated November 2026
Short answer
ACE inhibitors cause hyperkalemia because they lower angiotensin II, a main signal for aldosterone release. With less aldosterone, the collecting ducts of the kidney excrete less potassium. In healthy kidneys the rise is usually small; kidney disease, diabetes, potassium-sparing diuretics, potassium supplements or potassium salt substitutes can push it into a dangerous range.
The chain from blocked enzyme to retained potassium
Start with the enzyme. An ACE inhibitor stops angiotensin I from being converted to angiotensin II. Angiotensin II does two jobs that matter here: it tightens blood vessels, and it tells the adrenal cortex to release aldosterone. Block the first job and blood pressure falls, which is the reason the drug is prescribed. Block the second and aldosterone falls with it.
Aldosterone acts on the cortical collecting ducts. AAFP describes its effect as making those ducts retain sodium and excrete potassium. Less aldosterone means the kidney holds on to more potassium and lets a little more sodium go. So the potassium rise is not a toxic effect of the drug; it is the expected downstream result of the same pathway that lowers blood pressure.
Why the rise is usually small, and when it is not
For most people with normal kidneys the change is modest. The lisinopril label reports a mean rise of roughly 0.1 mEq/L in people treated for hypertension, though about 15 percent had a rise greater than 0.5 mEq/L. Healthy kidneys have other ways to excrete potassium, so a slightly lower aldosterone level is usually absorbed without trouble.
The danger appears when the backup routes are already weak. The label lists renal insufficiency and diabetes mellitus as risk factors. AAFP adds older age, since kidney function declines with age, and diabetic kidney disease with low renin and low aldosterone, where the system is already turned down before the drug arrives. In these clients, a small push from the ACE inhibitor lands on top of an existing problem.
Salt substitutes, ARBs and other add-ons that stack the risk
Many salt substitutes swap sodium chloride for potassium chloride. A client told to cut salt for blood pressure may reach for one and unknowingly take in a steady potassium load while the kidney is less able to clear it. The lisinopril label tells clinicians to instruct patients not to use potassium-containing salt substitutes without consulting their prescriber.
Drug combinations matter just as much. Potassium-sparing diuretics and potassium supplements both add to the problem, and the label advises frequent potassium monitoring with potassium-sparing diuretics. Combining an ACE inhibitor with an ARB or another renin-angiotensin blocker raises the risk of hyperkalemia, low blood pressure and kidney changes. NSAIDs can worsen kidney function, which removes yet another escape route for potassium.
What the nurse checks and reports
Before giving a dose, look at the most recent potassium and kidney function results, and at the medication list for potassium-sparing diuretics, supplements and NSAIDs. MSD Manuals describes the earliest ECG sign of rising potassium as peaked T waves, appearing once potassium is above about 5.5 mEq/L, so a new potassium result above the normal range on a client taking an ACE inhibitor is reported, not filed.
Teaching closes the loop at home. Clients should tell their prescriber before using a salt substitute or a potassium supplement, keep scheduled blood tests, and report muscle weakness or a new irregular or slow heartbeat. Whether to hold the next dose is a prescriber decision under local protocol, but the nurse is the one who notices the combination of findings and raises it.
Hypothetical practice scenario
Hypothetical scenario, not a real exam item: a 72-year-old client with type 2 diabetes and chronic kidney disease takes lisinopril and was recently started on spironolactone for heart failure. The morning potassium is 5.9 mEq/L. Which statement from the client is most concerning: "I take my pills with breakfast," "I switched to a low-sodium salt that my neighbor recommended," or "I feel a little dizzy when I stand up quickly"?
The salt substitute is the priority, because it is likely a potassium source added to two drugs that already reduce potassium excretion in a client with weak kidneys. The dizziness is real and worth assessing, but orthostatic lightheadedness is a known, lower-stakes effect of blood pressure drugs. Taking pills with breakfast is not a problem. The lesson is to look for the hidden potassium source in the history.
Sources and further reading
AAFP: Hyperkalemia (American Family Physician, 2006). Aldosterone makes cortical collecting ducts excrete potassium and retain sodium; ACE inhibitors and ARBs suppress aldosterone; risk factors including kidney disease, diabetic hyporeninemic hypoaldosteronism, potassium-sparing diuretics, NSAIDs, age, salt substitutes.
DailyMed: Lisinopril tablets label. Decreased aldosterone and small potassium rise (mean about 0.1 mEq/L, about 15 percent above 0.5 mEq/L); hyperkalemia risk factors; dual RAS blockade, potassium-sparing diuretic and NSAID interactions; salt substitute counseling.
MSD Manual Professional Version: Hyperkalemia. ACE inhibitors, ARBs and potassium-sparing diuretics as causes; peaked T waves once potassium exceeds about 5.5 mEq/L.
The next step on this is the same as on everything else here: answer questions and read the rationales. Our pharmacology practice questions are the closest set to what this page covers.
One question from the pharmacology set
A client with heart failure is started on furosemide 40 mg PO daily. Which findings should the nurse report to the provider before administering the next dose? Select all that apply.
Rationale
Furosemide is a loop diuretic, so the two things you are watching are potassium and kidney function. A potassium of 2.9 mEq/L is below the 3.5–5.0 reference range and puts the client at risk for dysrhythmia — hold and report. Muscle cramps with palpitations are the clinical face of that same hypokalemia, so they are reported together, not separately. A creatinine that doubles signals the diuresis has outrun renal perfusion. A blood pressure of 132/78 and a 1 kg loss are the expected response to the drug working, not reasons to hold it.
Answer: A, D, E
Common questions
Should salt substitutes be avoided on ACE inhibitors?
Many salt substitutes contain potassium chloride. The lisinopril label instructs clinicians to tell patients not to use potassium-containing salt substitutes without consulting their prescriber, because they add potassium while the drug reduces potassium excretion. The risk is highest with kidney disease or diabetes.
Do ARBs raise potassium too?
Yes. ARBs block the angiotensin II receptor instead of the converting enzyme, but the result is the same: lower aldosterone activity and less potassium excretion. AAFP groups both classes as causes of hyperkalemia, and using an ACE inhibitor and an ARB together increases the risk further.
Which clients on ACE inhibitors are most at risk for high potassium?
Clients with kidney impairment, diabetes or older age, and those also taking potassium-sparing diuretics, potassium supplements, potassium salt substitutes, NSAIDs or a second renin-angiotensin blocker such as an ARB. Each either adds potassium or removes another route the kidney uses to excrete it.
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