What are the side effects of losartan?

Side Effects of Losartan

Losartan is exceptionally well tolerated, with dizziness being the only side effect reported more frequently than placebo in clinical trials, and it has a significantly lower incidence of cough compared to ACE inhibitors. 1, 2

Common Side Effects

The most frequently reported adverse effects in clinical trials include:

For hypertension patients:

• Upper respiratory infection (6.5%) 2
• Dizziness (4.1%) – the only side effect considered drug-related more often than placebo (2.4% vs 1.3%) 2, 3
• Headache (14.1%) – though this occurred even more frequently with placebo (17.2%) 2
• Back pain 1
• Stuffy nose 1

For type 2 diabetes patients with diabetic kidney disease:

• Diarrhea 1
• Fatigue/tiredness 1
• Low blood sugar 1
• Chest pain 1

The overall discontinuation rate due to adverse effects with losartan monotherapy is remarkably low at 2.3%, which is actually lower than placebo (3.7%). 2, 3

Serious but Rare Side Effects

Life-threatening reactions:

• Angioedema – swelling of the face, lips, throat, or tongue requiring immediate emergency care and discontinuation of losartan 1, 4
• Anaphylactoid reactions 4

Cardiovascular effects:

• Hypotension (low blood pressure) causing faintness or dizziness; first-dose hypotension is uncommon with losartan 1, 2

Renal and electrolyte disturbances:

• Hyperkalemia (high potassium levels) – particularly in patients with chronic kidney disease, diabetes, or those taking potassium-sparing agents 1
• Worsening kidney function in patients with pre-existing renal problems, manifesting as swelling in feet/ankles/hands or unexplained weight gain 1

Metabolic and Laboratory Effects

Favorable metabolic profile:

• Losartan does not cause adverse metabolic effects such as decreased HDL cholesterol, increased triglycerides, or new-onset diabetes 5
• Uricosuric effect – losartan lowers serum uric acid levels, which may be beneficial when combined with thiazide diuretics but could theoretically lead to uric acid stone formation 5, 4

No clinically relevant laboratory abnormalities have been documented during losartan therapy, and renal function is preserved in patients with or without renal insufficiency. 6

Unique Tolerability Advantages

Cough incidence:

• Dry cough occurs in only 3.1% of losartan patients versus 8.8% of ACE inhibitor patients (P < 0.001) 2, 3
• The incidence of cough with losartan is similar to placebo (2.6%) 2, 3
• Losartan has a significantly lower incidence of cough compared to ACE inhibitors 5

Musculoskeletal effects:

• Myopathy is not a known adverse effect of losartan 5

Rare Neurological Effects

One case report documented tremors and dysarthria occurring one hour after losartan administration, severe enough to require hospitalization, though symptoms resolved without targeted treatment. 7 This represents an isolated case and is not an established side effect.

Absolute Contraindications

Pregnancy:

• Losartan can cause fetal harm or death throughout all trimesters, including renal dysfunction, oligohydramnios, skull hypoplasia, and fetal death 1
• Discontinue immediately upon pregnancy detection 1

Drug interactions:

• Never combine with ACE inhibitors or aliskiren (in diabetic patients), as this increases hyperkalemia, syncope, and acute kidney injury risk 2–3-fold without added benefit 8, 1

Monitoring Requirements

Essential monitoring parameters:

• Serum creatinine/eGFR and potassium within 1–2 weeks after initiation or dose changes, then at least annually 8
• Blood pressure monitoring every 2–4 weeks during titration 8
• More frequent monitoring in patients with chronic kidney disease, diabetes, or those receiving potassium-sparing agents 8

Common Pitfalls to Avoid

• Do not assume cough is from losartan; the incidence is equivalent to placebo 2, 3
• Do not discontinue prematurely for mild hyperkalemia; implement potassium-lowering strategies first 8
• Do not combine with NSAIDs, as they may blunt antihypertensive effect and worsen renal function 8
• Monitor lithium levels if co-administered, as losartan can precipitate lithium toxicity 8
• Avoid potassium supplements or salt substitutes containing potassium, especially in high-risk patients 1