Losartan belongs to a family of medications known as angiotensin II receptor blockers. These medications are used in adults and children over the age of six to lower mild-to-moderate hypertension (high blood pressure).

Angiotensin II is a chemical that the body releases to cause the constriction of blood vessels. Losartan blocks the action of angiotensin II, resulting in the relaxation of the blood vessels. This relaxation causes the blood pressure to drop. The full effects of losartan are usually seen within 3 to 6 weeks after treatment has started. Losartan may be used alone or in combination with a diuretic (water pill).

Losartan may also be taken by adults who have type 2 diabetes along with hypertension and protein in the urine (proteinuria). In these cases, losartan is used to protect the kidneys from further damage due to diabetes.

This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

The usual recommended dose of losartan for adults is 50 mg or 100 mg once daily. The usual starting dose is 50 mg once daily. In some cases, a lower starting dose of 25 mg once daily may be advisable. Do not take more than 100 mg once daily. Your doctor will adjust the dosage according to individual needs.

The usual recommended dose of losartan for children, aged 6 - 16 years, is based on body weight. The dose is 25 mg once daily for children weighing between 20 kg and 49 kg. This dose may be increased to 50 mg once daily. In children weighing more than 50 kg, the starting dose is 50 mg taken once daily. This dose may be increased to 100 mg once daily.

Losartan may be taken with or without food, but should be taken the same way each day.

Many things can affect the dose of a medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones listed here, do not change the way that you are taking the medication without consulting your doctor.

It is important that this medication be taken exactly as prescribed by your doctor. If you miss a dose, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Do not use this medication if you:

• are allergic to losartan or any ingredients of the medication
• have diabetes or moderate-to-severe kidney disease and are taking the medication aliskiren

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent. The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

• back or leg pain
• changed sense of taste
• diarrhea
• dizziness
• fatigue
• headache
• muscle cramps
• vomiting

Although most of these side effects listed below don't happen very often, they could lead to serious problems if you do not check with your doctor or seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

• fainting or dizziness when rising from a sitting or lying position
• signs of clotting problems (e.g., unusual nosebleeds, bruising, blood in urine, coughing blood, bleeding gums, cuts that don't stop bleeding)
• signs of kidney problems (e.g., change in the amount or colour of urine, increased urination at night, blood in the urine, swelling in the feet or legs)
• signs of liver problems (e.g., nausea, vomiting, diarrhea, loss of appetite, weight loss, yellowing of the skin or whites of the eyes, dark urine, pale stools)
• signs of too much potassium in the body (e.g., irregular heartbeat, muscle weakness, generally feeling unwell)
• unexplained muscle pain, weakness, or dark brown urine

Stop taking the medication and seek immediate medical attention if any of the following occur:

• signs of a serious allergic reaction (e.g., swelling of face or throat, hives, or difficulty breathing)

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.

Blood pressure: Occasionally, a larger-than-expected drop in blood pressure occurs after taking losartan, in some cases after the first dose. It is more likely to occur if you take diuretics (water pills) or the medication aliskiren, have reduced salt intake, are on dialysis, or are experiencing diarrhea or vomiting. Blood pressure should be checked more often in these situations. If you have low blood pressure or are just starting to take this medication, you should move slowly when you are rising from a reclining to an upright position to reduce the risk of dizziness.

Dizziness: Losartan may cause dizziness, affecting your ability to drive or operate machinery. Avoid these and other hazardous tasks until you have determined how this medication affects you.

Kidney problems: The use of losartan may affect the function of the kidneys, especially for those who already have kidney problems. Certain people have experienced changes in kidney function (e.g., people with narrowed blood vessels in their kidneys, or those with severe congestive heart failure). The use of diuretics (water pills), nonsteroidal anti-inflammatory drugs (NSAIDs) or aliskiren may further increase risk of kidney problems for people already at risk for this problem. If you have kidney function problems, your doctor will likely closely monitor your condition while you are taking this medication.

Liver function: Losartan is removed from the body by the liver. Liver disease or reduced liver function may cause this medication to build up in the body, causing side effects. If you have liver problems, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed. Your doctor may want to test your liver function regularly with blood tests while you are taking this medication.

Potassium: Increases in blood levels of potassium can occur with use of this medication. This rarely causes problems, but your doctor may want to monitor your potassium levels through blood tests.

Pregnancy: Losartan should not be taken by pregnant women as it can cause severe harm or death to an unborn child. If you are planning to become pregnant, discuss alternative medications for blood pressure control with your doctor.

If you become pregnant while taking this medication, stop taking it and tell your doctor at once.

Breast-feeding: It is not known if losartan passes into breast milk. If you are a breast-feeding mother and are taking this medication, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: The safety and effectiveness of using this medication have not been established for children less than 6 years of age.

There may be an interaction between losartan and any of the following:

• aldesleukin
• aldosterone antagonists (e.g., eplerenone, finerenone, spironolactone)
• aliskiren
• alpha-agonists (e.g., clonidine, methyldopa)
• alpha-blockers (e.g., alfuzosin, tamsulosin)
• amiodarone
• amphetamines (e.g., dextroamphetamine)
• angiotensin converting enzyme inhibitors (ACEIs; e.g., captopril, lisinopril, ramipril)
• other angiotensin receptor blockers (ARBs; e.g., candesartan, irbesartan)
• antipsychotics (e.g., cariprazine, chlorpromazine, clozapine, haloperidol, olanzapine, quetiapine, risperidone)
• apomorphine
• barbiturates (e.g., butalbital, phenobarbital)
• bortezomib
• brimonidine
• bromocriptine
• calcium channel blockers (e.g., amlodipine, diltiazem, nifedipine, verapamil)
• celecoxib
• CF transmembrane regulators (e.g., ivacaftor, lumacaftor)
• conivaptan
• diuretics (water pills; e.g., bumetanide, furosemide)
• drospirenone
• duloxetine
• fluconazole
• flunarizine
• general anesthetics (medications used to put people to sleep before surgery)
• heparin and low-molecular weight heparins (e.g., dalteparin, tinzaparin)
• iron sucrose
• levodopa
• lithium
• methylphenidate
• mifepristone
• monoamine oxidase inhibitors (MAOIs; e.g., phenelzine, rasagiline, selegiline, tranylcypromine)
• medications that increase the level of potassium in the blood (e.g., spironolactone, amiloride, triamterene, or salt substitutes that contain potassium)
• mifepristone
• minoxidil
• morphine
• nabilone
• nitrates (e.g., nitroglycerin, isosorbide dinitrate, isosorbide mononitrate)
• non-steroidal anti-inflammatory medications (NSAIDs; e.g., diclofenac, ibuprofen, ketorolac, naproxen)
• obinutuzumab
• pentoxifylline
• phosphodiesterase 5 inhibitors (e.g., sildenafil, tadalafil, vardenafil)
• pramipexole
• primidone
• certain protein kinase inhibitors (e.g., asciminib, brigatinib)
• ranolazine
• riociguat
• ropinirole
• rotigotine
• sacubitril
• sodium phosphates
• sotalol
• tacrolimus
• tizanidine
• tolvaptan
• tretinoin
• tricyclic antidepressants (e.g., clomipramine, imipramine)
• trimethoprim
• yohimbine

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.