Losartan: what it treats, how to take it, side effects
Last updated September 3, 2026.
Losartan is a blood pressure medication that relaxes your blood vessels by blocking a natural vessel-tightening signal. You may know it as Cozaar. It belongs to the angiotensin II receptor blocker (ARB) class, and it controls high blood pressure rather than curing it - which makes it a long-term daily habit.
What does it treat?
High blood pressure, alone or with other medications. It also decreases stroke risk in people with high blood pressure plus left ventricular hypertrophy (MedlinePlus notes it may not reduce that risk in African Americans with these conditions), and it treats kidney disease in people with type 2 diabetes and high blood pressure. It is sometimes used for heart failure too.
How do you take it?
As a tablet, usually once or twice a day, with or without food, at the same time every day. The label's usual adult dose is 50 mg once daily, increased to 100 mg if more blood pressure response is needed; your doctor will start low and adjust up. Patience: blood pressure may drop in the first week, but the full benefit takes 3 to 6 weeks. Keep taking it even when you feel well - controlled pressure is the drug working, not the problem being gone. Missed dose: take it when you remember unless the next one is close; never double up.
Side effects to know
- Common: leg, knee, or back pain, muscle cramps or weakness, diarrhea, heartburn, and decreased sensitivity to touch. Dizziness and lightheadedness when standing up too fast are common early on - get out of bed slowly.
- Serious: swelling of the face, throat, tongue, lips, eyes, hands, feet, ankles, or lower legs, hoarseness, difficulty breathing or swallowing, and chest pain mean calling your doctor immediately. Vomiting, diarrhea, heavy sweating, or not drinking enough fluids can drop your pressure too far - tell your doctor if those hit.
Who should not take it?
Pregnancy is the hard stop, and the label boxes it: do not take losartan if you are pregnant, and if you become pregnant while taking it, stop and call your doctor immediately - it can cause death or serious injury to the fetus in the last 6 months of pregnancy. Tell your doctor if you are breastfeeding. The aliskiren combination is another rule: if you have diabetes and take aliskiren, your doctor will probably say no. Flag heart failure and kidney or liver disease. Two everyday traps: NSAIDs like ibuprofen and naproxen and aspirin can interfere, and potassium supplements and potassium-based salt substitutes can push your potassium too high - do not start any of them without asking.
When is it an emergency?
Call 911 for facial or throat swelling, trouble breathing or swallowing, or fainting. Chest pain on this medication is a same-day call at minimum. For an overdose, call Poison Control at 1-800-222-1222. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
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Common questions
Why can't I take losartan while pregnant?
The label carries a boxed warning: losartan may cause death or serious injury to the fetus when taken in the last 6 months of pregnancy. MedlinePlus is direct - do not take it if you are pregnant, and if you become pregnant while taking it, stop and call your doctor immediately. If pregnancy is possible, your doctor picks a pressure medication with that in mind.
How long does losartan take to lower blood pressure?
First effects within the first week, full benefit in 3 to 6 weeks, per MedlinePlus. Do not judge the dose by the first few days - your doctor starts low and adjusts upward based on later readings.
Can I use salt substitutes while taking losartan?
Not without asking. MedlinePlus says do not use salt substitutes containing potassium without talking to your doctor - losartan already raises potassium, and the combination can push it too high. Regular salt in moderation is the safer default, and a low-sodium diet if your doctor prescribes one.
Can I take ibuprofen with losartan?
Not without your doctor's say-so. MedlinePlus lists aspirin and NSAIDs like ibuprofen and naproxen as interacting with losartan - they can blunt its blood pressure effect and strain the kidneys. For a headache, ask your pharmacist what fits your regimen.
Why do I feel dizzy when I stand up on losartan?
Your blood pressure adjusting. MedlinePlus says losartan may cause dizziness, lightheadedness, and fainting when you get up too quickly from a lying position, especially when you first start. Get out of bed slowly and rest your feet on the floor before standing. It usually settles; if it does not, tell your doctor.
Can I drink alcohol while taking losartan?
Neither the FDA label nor MedlinePlus lists a specific alcohol interaction. MedlinePlus's lifestyle guidance for blood pressure includes using alcohol in moderation - alcohol raises blood pressure and can deepen the dizziness this drug can cause, so modesty serves you twice here.