How Long Does Losartan Take To Work?

In our latest question and answer, our pharmacist discusses how long it takes losartan to start working to reduce blood pressure.


How long does it take for losartan to start taking effect on high blood pressure?

Asked by Alex On May 18, 2023

Answered by
Medical Content Reviewed By HelloPharmacist Staff

Published May 18, 2023
Last updated Feb 23, 2024

Key points

  • Losartan begins to work right away, with your first dose, to lower blood pressure, but it will take at least 4 weeks to realize the full effect of the medication.
  • Depending on how high your blood pressure is, your doctor will re-evaluate you and how losartan is working to lower your blood pressure around 4 weeks after starting the medication.


Losartan (generic for Cozaar) will begin to work right away in regard to lowering your blood pressure, which is why some folks experience certain side effects, like, dizziness and lightheadedness, when therapy is started.

However, depending on how high your blood pressure is when you started the drug, your doctor will generally reevaluate you and your therapy needs after around 4 weeks of consistent dosing. At this point they will determine whether or not additional interventions need to be made for you.

Detailed Information

Losartan is an angiotensin II receptor antagonist, a drug class commonly referred to as an 'ARB' (angiotensin II receptor blocker). ARBs are commonly used to treat hypertension (high blood pressure) and work by blocking the action of a hormone that causes blood vessels to narrow, thus helping to relax and widen the blood vessels.

As mentioned in the first section, losartan will begin working with the first dose, but full effects will generally take at least a few weeks.

When you first start taking losartan, your pharmacist should warn you about some common side effects, many of which are related to an initial drop in blood pressure.

These side effects include dizziness, lightheadedness, and 'orthostatic hypotension', which signifies a drop in blood pressure when you change positions, especially when you stand up from a sitting or lying down position.

Being Re-Evaluated After Starting Losartan

According to the American College of Cardiology (ACC)/American Heart Association (AHA) 2017 hypertension guideline, individuals who are treated with antihypertensive drugs, like losartan, should be evaluated every four weeks or so until their blood pressure reaches the target goal.

In other words, after you start taking losartan, your doctor will likely reevaluate your blood pressure, and how the drug is working for you, after about 4 weeks. The reason for this timeframe is that it allows enough time for long-acting antihypertensive drugs like losartan to manifest their full blood pressure-lowering effect while keeping in mind that many individuals require additional interventions if blood pressure is still not at goal.

It should be noted, however, for patients with severely elevated blood pressure, reevaluating at two weeks or even sooner may be necessary.

Below is a flowchart provided from the AHA hypertension guidelines I have hyperlinked above, showing the recommendation for a re-evaluation timeframe of 4 weeks:

When to reassess bp after starting losartan

Source: 2017 ACC/AHA/AAPA/ABC/ACPM/AGS/APhA/ASH/ASPC/NMA/PCNA Guideline for the Prevention, Detection, Evaluation, and Management of High Blood Pressure in Adults

Will Losartan Itself Help You Reach A Normal Blood Pressure?

It's important to remember that achieving blood pressure control can be a gradual process. Depending on how high your blood pressure is and how your body responds to losartan, it may take some time to determine the appropriate dosage and its effectiveness for you personally and everyone's response to medications can vary.

It's also important to point out that many studies show that only 25-50% of individuals achieve blood pressure control with lifestyle modifications and monotherapy (i.e., only one blood pressure medication) alone. Oftentimes, additional medications need to be added on if you aren't able to reach your goal blood pressure with one medication and changes to your lifestyle.

Be sure to keep regular appointments with your doctor and keep in touch with them regarding how you are doing in reaching your blood pressure goals.

Final Words

I hope you found this helpful! Be sure to contact us again anytime!


  • 2017 ACC/AHA/AAPA/ABC/ACPM/AGS/APhA/ASH/ASPC/NMA/PCNA Guideline for the Prevention, Detection, Evaluation, and Management of High Blood Pressure in Adults: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines, PubMed
  • Cozaar Prescribing Information, AccessFDA

About the Pharmacist

Dr. Brian Staiger, PharmD

Dr. Brian has been practicing pharmacy for over 13 years and has wide-ranging experiences in many different areas of the profession. From retail, clinical, program development, and administrative responsibilities, he's your knowledgeable and go-to source for all your pharmacy and medication-related questions! Dr. Brian Staiger also has herbalist training and educational certificates in the field of medical ethnobotany. Feel free to send him an email at [email protected]! You can also connect with Dr. Brian Staiger on LinkedIn.

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