Losartan Causes HYPERkalemia, Not Hypokalemia
No, losartan does NOT cause potassium drops—it does the exact opposite by raising potassium levels and can cause hyperkalemia. If you're experiencing hypokalemia (low potassium) while on losartan, the medication is not the culprit, and you need to look for other causes 1.
Why Losartan Raises Potassium
Losartan is an angiotensin II receptor blocker (ARB) that blocks aldosterone production, which reduces potassium excretion in the kidneys, leading to elevated serum potassium levels 2. This is a class effect shared by all RAAS inhibitors (ACE inhibitors, ARBs, and aldosterone antagonists) 1.
- In hypertensive patients without risk factors, the incidence of hyperkalemia with ARB monotherapy like losartan is less than 2% 2
- Losartan typically increases serum potassium by approximately 1 mEq/L 3
- The European Society of Cardiology explicitly lists ARBs including losartan among medications that cause hyperkalemia, not hypokalemia 1
What Actually Causes Low Potassium
If your potassium is dropping while on losartan, consider these alternative explanations:
Loop or thiazide diuretics are the most common culprits for hypokalemia and are frequently prescribed alongside losartan for hypertension or heart failure 1. The combination of losartan with hydrochlorothiazide is particularly common 4.
Other potential causes of your low potassium include:
- Inadequate dietary potassium intake
- Gastrointestinal losses (diarrhea, vomiting)
- Other medications (not losartan)
- Renal tubular disorders
- Hyperaldosteronism (though losartan would partially counteract this)
Clinical Context: The Balancing Act
Interestingly, one early study in normotensive subjects found that losartan produced a transient rise in urinary potassium excretion 5, but this is not the sustained effect seen clinically. The dominant and clinically relevant effect of losartan is potassium retention, not loss 1, 2.
Common clinical scenario: Patients are often prescribed losartan alongside a thiazide or loop diuretic. The diuretic causes potassium loss, while losartan causes potassium retention—these effects partially offset each other 6. If you're on this combination and experiencing hypokalemia, the diuretic effect is overwhelming losartan's potassium-retaining effect.
What You Should Do
Check your complete medication list for diuretics or other potassium-wasting medications 1. If you're on a diuretic, that's almost certainly causing your low potassium, not the losartan.
Monitor your potassium levels within 1-2 weeks after any dose changes, especially if you have chronic kidney disease or diabetes 2, 3.
Do not stop losartan based on a misunderstanding about its effects on potassium—it provides significant cardiovascular and renal protection that outweighs the risk of hyperkalemia when properly monitored 1, 3.