Losartan is a human blood pressure medication that, fortunately, tends to be less dangerous to dogs than many other prescription drugs. Dogs absorb losartan poorly and don’t convert it into the active form that makes it effective in people, so small amounts often cause little to no harm. That said, larger doses can drop your dog’s blood pressure to dangerous levels, and the situation always warrants a call to your vet or a poison control hotline.
Why Losartan Is Less Potent in Dogs
In humans, the liver converts losartan into an active compound that does most of the blood-pressure-lowering work. Dogs don’t produce this metabolite. Their bodies also absorb only about 23 to 33 percent of the drug orally, and it clears quickly with a half-life of roughly 1.8 to 2.5 hours. This means losartan has little pharmacological activity in dogs unless a large amount is ingested.
This doesn’t mean you can ignore the situation. At high enough doses, even the parent drug can lower blood pressure, and individual factors like your dog’s size, age, and kidney health all affect risk.
Signs to Watch For
If losartan does affect your dog, symptoms typically appear within a few hours. The primary concern is abnormally low blood pressure, which can show up as:
- Weakness or lethargy: your dog may seem unsteady, reluctant to stand, or unusually tired
- Vomiting
- Pale gums (check by pressing a finger against the gum and seeing if color returns slowly)
- Abnormal heart rate, either faster or slower than usual
Severely low blood pressure can reduce blood flow to the kidneys, potentially causing secondary kidney damage. This is the most serious complication and is more likely if your dog already has kidney disease or heart problems.
How Much Is Dangerous
As a general guideline for blood pressure medications in this class, ingestions above 20 mg per kilogram of body weight are considered concerning. To put that in perspective, a 20-pound dog (about 9 kg) would need to eat roughly 180 mg or more to reach that threshold. Since losartan tablets commonly come in 25, 50, or 100 mg sizes, a single low-dose tablet is unlikely to cause serious problems in a medium or large dog. A small dog eating multiple tablets is a different story.
Dogs that are otherwise healthy and eat a small amount relative to their body weight can often be monitored at home under guidance from a veterinarian or poison control. Dogs with pre-existing kidney failure or heart disease face higher risk even at lower doses.
What to Do Right Away
Call your veterinarian or an emergency veterinary clinic immediately. If you can’t reach one, contact the ASPCA Poison Control Hotline at 888-426-4435 or the Pet Poison Helpline at 855-764-7661 (both charge a consultation fee but are available 24/7).
Before you call, gather as much information as you can: the strength of the tablets (printed on the bottle), how many are missing, when your dog ate them, and your dog’s approximate weight. This helps the vet or poison control specialist calculate whether your dog reached a concerning dose and decide on next steps.
Do not try to make your dog vomit unless specifically told to do so. Inducing vomiting is sometimes the right call, but in other situations it can cause more harm. A professional can tell you whether it’s appropriate based on how much time has passed and what your dog swallowed.
What Happens at the Vet
If your vet recommends bringing your dog in, the visit typically focuses on preventing further absorption and supporting blood pressure. If the ingestion was recent (usually within the last one to two hours), the vet may induce vomiting or administer activated charcoal to limit how much drug enters the bloodstream.
Your dog’s blood pressure and heart rate will be monitored. In cases where blood pressure drops significantly, intravenous fluids help restore circulation and protect the kidneys. Blood work may be checked to assess kidney function, particularly if your dog ate a large amount or has underlying health issues.
Because losartan clears a dog’s system relatively quickly, most symptoms resolve within several hours. Dogs that receive prompt treatment and don’t develop kidney complications generally recover fully. The short half-life of the drug works in your dog’s favor here, as its effects don’t linger the way some other medications can.
Higher Risk Situations
A few factors make losartan ingestion more worrisome. Very small dogs face higher risk simply because the same tablet represents a much larger dose per kilogram. A 100 mg tablet that barely registers in a 70-pound Labrador could push a 5-pound Chihuahua well past the danger zone.
Dogs with existing kidney disease are more vulnerable because their kidneys already have reduced capacity. Even a modest drop in blood pressure can further compromise kidney function in these animals. The same applies to dogs already taking heart or blood pressure medications, since losartan can amplify their effects.
Puppies and senior dogs also deserve extra caution. Their bodies may be less equipped to compensate for sudden changes in blood pressure, making them more likely to show symptoms at lower doses.