Prescription ·Strong evidence ·Reviewed May 2026
Losartan/hydrochlorothiazide is a fixed-dose combination antihypertensive that pairs the angiotensin II receptor blocker (ARB) losartan with the thiazide diuretic hydrochlorothiazide. It is used to treat hypertension in patients who are not adequately controlled on either agent alone, or as initial therapy when blood pressure goals warrant two complementary mechanisms. The two components act on different pathways, and losartan partially offsets the potassium loss caused by hydrochlorothiazide.
The bottom line
Evidence rating strong. Most-documented uses: treatment of hypertension (high blood pressure), blood pressure control when monotherapy is insufficient, reduction of cardiovascular and stroke risk associated with lowering elevated blood pressure. 3 sources indexed (2002–2019), with 5 interaction records on file.
Core mechanism
Losartan selectively blocks the binding of angiotensin II to the angiotensin II type 1 (AT1) receptor, preventing angiotensin II-mediated vasoconstriction and reducing aldosterone secretion, which lowers blood pressure and tends to conserve potassium. Hydrochlorothiazide inhibits the sodium-chloride cotransporter in the distal convoluted tubule of the nephron, increasing urinary excretion of sodium and water and producing a diuretic and antihypertensive effect; over time it also reduces peripheral vascular resistance. Hydrochlorothiazide increases distal sodium delivery and aldosterone activity, promoting urinary potassium and magnesium loss, while losartan's suppression of aldosterone tends to blunt the thiazide-induced kaliuresis, so the combination produces a smaller net change in serum potassium than either drug would alone.1,2
Can be taken with or without food. Food does not meaningfully affect the antihypertensive effect of either component. Taking the dose in the morning is often preferred to limit nocturnal diuresis. Losartan is converted to an active carboxylic acid metabolite (E-3174) that contributes most of the AT1 receptor blockade.2,3
Nutrients this medication can lower over time, and what to replace.
Hydrochlorothiazide increases urinary potassium loss, although losartan may offset or reverse this in some patients.
Thiazide diuretics can increase urinary magnesium loss.
Thiazide diuretics increase urinary zinc excretion through enhanced distal tubular fluid flow and reduced zinc reabsorption, which can lower body zinc stores over long-term use.
As a natriuretic agent, hydrochlorothiazide directly increases renal sodium excretion; combined with reduced thirst or low sodium intake in older adults this can produce hyponatremia. This is an intended pharmacologic effect rather than a nutritional deficiency, but symptomatic hyponatremia is a recognized adverse outcome.
Potassium supplements can cause hyperkalemia from losartan even though hydrochlorothiazide can lower potassium in some patients.
Recommendation: Use potassium only with lab monitoring; do not assume the thiazide component makes potassium supplementation safe.
Losartan/Hydrochlorothiazide can lower magnesium in some patients, and magnesium replacement may be needed when deficiency is documented.
Recommendation: Monitor magnesium when clinically indicated and supplement only to a target range, especially in kidney disease.
Hydrochlorothiazide decreases urinary calcium excretion; high-dose calcium can contribute to hypercalcemia in susceptible patients.
Recommendation: Avoid excessive calcium supplementation and monitor calcium if using high doses or vitamin D, or if kidney disease or hyperparathyroidism is present.
Vitamin D3 increases intestinal calcium absorption. Combined with hydrochlorothiazide's calcium-sparing effect on the kidney, high-dose vitamin D can elevate serum calcium and precipitate hypercalcemia, particularly when calcium supplements are also used. The risk is dose-dependent and greater in patients with hyperparathyroidism or reduced renal function.
Recommendation: Standard maintenance vitamin D doses are generally acceptable, but avoid high-dose vitamin D alongside this thiazide-containing combination without monitoring serum calcium, especially if calcium supplements are co-administered. Watch for symptoms of hypercalcemia.
Garlic extract has a modest blood-pressure-lowering effect in hypertensive patients. When added to an effective antihypertensive combination such as losartan plus hydrochlorothiazide, the cumulative effect is usually small but can occasionally produce additive hypotension, particularly in volume-depleted patients or after dose escalation of the medication.
Recommendation: Garlic extract is generally compatible with this combination and is unlikely to cause problems at culinary or standard supplement doses. Patients should monitor for dizziness or lightheadedness, especially when starting therapy or when the diuretic causes volume loss, and report sustained low readings to their clinician.
Search all 5 interaction records for Losartan/Hydrochlorothiazide →
Numbered references. Citations throughout the page link here.
Losartan-based therapy reduced the composite of cardiovascular death, stroke, and myocardial infarction, driven mainly by a significant reduction in stroke, compared with atenolol-based therapy at similar blood pressure reductions.
Hydrochlorothiazide increases distal sodium delivery and promotes kaliuresis and magnesium wasting; combining it with a renin-angiotensin system blocker mitigates but does not eliminate hypokalemia risk.
Fixed-dose losartan/HCTZ lowers blood pressure additively; losartan attenuates the hypokalemic effect of hydrochlorothiazide, and the combination is contraindicated in pregnancy.
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