The Short Answer
Losartan (sold as Cozaar) leaves your blood fast. The parent drug has a half-life of only about 2 hours. But your liver turns losartan into an active metabolite called EXP3174 that is far stronger and lasts longer, with a half-life of about 6 to 9 hours. That metabolite is what keeps your blood pressure down all day. Losartan and its metabolite are essentially out of your system in roughly 1 to 2 days.
This article is for general information only. Consult your doctor or pharmacist for advice specific to your medications.
Why "How Long It Stays" Is Not "How Long It Works"
Most articles answer this with one number, and that misses the point. There are two different timelines: how long losartan is physically in your blood, and how long it keeps lowering your blood pressure. For losartan, those answers are very different.
The reason is a chemical called EXP3174, also written E-3174. It is losartan's active metabolite, a new compound your liver makes after you swallow the pill. According to the FDA prescribing information on DailyMed, this metabolite is 10 to 40 times more potent by weight than losartan itself. So the pill that leaves your body quickly is not really the medicine doing the work.
Two Timelines: Drug Present vs. Drug Working
Losartan works in two stages. The parent drug peaks in your blood about 1 hour after a dose, then drops quickly. The FDA label lists its terminal half-life at about 2 hours, so losartan itself is mostly gone within a single afternoon.
While that is happening, your liver converts part of the dose into EXP3174. This metabolite peaks about 3 to 4 hours after your dose and has a half-life of about 6 to 9 hours. It also clears far more slowly: the label gives a plasma clearance of about 600 mL/min for losartan versus only about 50 mL/min for the metabolite. A human study by Lo and colleagues in Clinical Pharmacology & Therapeutics, 1995 measured this in 18 healthy adults and found the metabolite's total exposure was about four times that of losartan. The active metabolite dominates. That is the medicine actually controlling your blood pressure.
The EXP3174 Metabolite: The Part Other Articles Miss
Losartan works once a day not because the pill lasts all day, but because EXP3174 does. Losartan is an angiotensin II receptor blocker, or ARB, that lowers blood pressure by blocking a receptor that would otherwise tighten your blood vessels. EXP3174 blocks that same receptor, but holds on more tightly and for longer. A review by Ripley and Hirsch in the International Journal of Nephrology and Renovascular Disease, 2010 confirms the active metabolite is "10-40 times more potent by weight than the parent molecule losartan" and is formed by the liver enzymes CYP2C9 and CYP3A4.
The takeaway is reassuring. The pill leaves fast, but the medicine that lowers your pressure stays much longer, which is why one late or missed dose does not leave you instantly unprotected. For what to do when timing slips, see our guide on a missed dose of losartan.
The 5-Half-Life Clearance Timeline
A drug is essentially cleared after about 5 half-lives. Because the active metabolite is the slower part, the table below uses its longer half-life range as a safe planning window.
| Half-lives elapsed | Time after last dose | Approximate metabolite remaining |
|---|---|---|
| 1 | About 6 to 9 hours | 50% |
| 2 | About 12 to 18 hours | 25% |
| 3 | About 18 to 27 hours | 12.5% |
| 4 | About 24 to 36 hours | 6.25% |
| 5 | About 30 to 45 hours | About 3% (essentially cleared) |
These are approximate ranges. The parent losartan, with its 2-hour half-life, is gone much sooner, usually within about 10 hours. Together, losartan and its active metabolite are essentially out of your system in roughly 1 to 2 days.
What Speeds Up or Slows Down Clearance
The timeline is not the same for everyone. Your genetics matter: losartan is converted to its active metabolite by the liver enzyme CYP2C9, and people carry different versions of that gene. A 2021 systematic review in the Journal of Personalized Medicine found that carriers of the CYP2C9*2 and *3 variants had higher losartan levels and lower metabolite levels, so how fast you make the working form can differ from person to person.
Liver function matters too, since the liver does the conversion. Kidneys play a part as well, but losartan leaves the body through more than one route: the FDA label reports about 35% of a dose is recovered in urine and about 60% in feces. Because elimination is mixed, kidney issues alone do not stall clearance the way they would for a drug cleared only by the kidneys. Food slows how fast losartan is absorbed but barely changes the total amount your body takes in, so you can take it with or without food.
When This Timeline Actually Matters
Most days you do not need to think about losartan's half-life. A few moments are exceptions.
If you and your doctor decide to move losartan from morning to night, the long-acting metabolite makes the switch smooth, since EXP3174 is still working from your previous dose. Our article on whether you can take losartan twice a day explains how the half-life shapes once-daily versus twice-daily schedules, and the best time to take losartan guide covers timing.
After a missed dose, the 6 to 9 hour metabolite half-life is why your blood pressure usually does not spike right away. The general label guidance is to take a missed dose when you remember, unless it is close to your next dose, in which case you skip it. Never double up to catch up. If you did take extra by accident, the metabolite clears over roughly 1 to 2 days; our accidental double dose of losartan and class-level blood pressure medication double-dose guides cover what to watch for.
Not every ARB clears on the same schedule, which is one reason your doctor might pick one over another. Olmesartan, for example, has a longer half-life than losartan. See our best time to take olmesartan guide for how a sister ARB compares.
Related half-life guides: the parent-versus-metabolite split is unique to each drug, so compare how long your other prescriptions linger in how long amlodipine stays in your system, how long omeprazole stays in your system, and how long atorvastatin stays in your system.
How Pillo Helps
Losartan is a once-daily medication, which sounds easy until a busy week scrambles your routine. Pillo sends a persistent reminder that keeps going until you confirm the dose, so a skipped Tuesday does not quietly become a skipped week. Pillo also keeps a record of when you took each dose, useful information to share with your pharmacist if you are adjusting your timing. Pillo is available on Android. Download Pillo on Google Play.
FAQ
Does losartan leave your system faster if you stop taking it?
No. Stopping does not speed up clearance. After your last dose, losartan itself clears within about 10 hours, and the active metabolite is essentially gone within roughly 1 to 2 days. The rate is set by your body's enzymes, not by whether you keep taking the drug.
Will I feel losartan wear off during the day?
Usually not. The active metabolite EXP3174 has a 6 to 9 hour half-life and is 10 to 40 times more potent, so it keeps your blood pressure controlled across a once-daily dose. If you do feel symptoms between doses, tell your doctor rather than changing your schedule yourself.
Should I take losartan in the morning or at night?
Either can work, because the long-acting metabolite covers the full day. The best time is the one you can take consistently. Some people are advised to take it at night, but that is an individual decision for your doctor.
Does food change how long losartan stays in your system?
Food slows how fast losartan is absorbed and lowers its peak level, but it barely changes the total amount your body takes in or how long the active metabolite lasts. You can take losartan with or without food.
How long after stopping losartan does blood pressure go back up?
The drug is mostly cleared in 1 to 2 days, but your blood pressure response depends on you, not just the drug. Many people see their pressure drift back toward its old level over several days. Never stop a blood pressure medication on your own. Talk to your doctor first.
A Note on Medical Advice
This article provides general information about how losartan is processed by the body and is not a substitute for professional medical advice. Always consult your doctor or pharmacist before stopping, switching, or adjusting any prescription medication.
