Incurin is an FDA-approved medication used to treat urinary incontinence in spayed female dogs. Its active ingredient is estriol, a naturally occurring form of estrogen that helps restore muscle tone to the urethral sphincter, the ring of muscle that keeps urine from leaking out. It’s given as a daily oral tablet and is the only estriol product specifically approved for dogs in the United States.
Why Spayed Dogs Develop Incontinence
When a female dog is spayed, her ovaries are removed, and her body stops producing the estrogen that previously helped keep the urethral sphincter firm and responsive. Over time, this drop in estrogen causes the sphincter to weaken. The result is what veterinarians call estrogen-responsive urinary incontinence: urine leaks out involuntarily, often while the dog is sleeping or resting. You might notice wet spots on bedding or damp fur around the hind legs.
This is one of the most common conditions in spayed dogs, particularly in medium and large breeds. It can develop months or years after the spay surgery. It’s not a behavioral issue or a housetraining problem. The dog simply can’t feel or control the leakage.
How Incurin Works
Estriol replaces some of the estrogen the dog’s body no longer makes. Research shows that estriol increases urethral resistance, meaning it tightens and strengthens the sphincter muscle so it can hold urine more effectively. In urodynamic studies, dogs treated with estriol showed significant increases in urethral pressure measurements within seven days of starting treatment.
Notably, estriol is a weaker and shorter-acting form of estrogen compared to other types. This is actually an advantage: it provides enough hormonal support to improve sphincter function without the stronger systemic effects that come with more potent estrogen compounds. The drug works locally on the urethral tissues rather than broadly affecting the entire body.
Which Dogs Can Take It
Incurin is specifically approved for ovariohysterectomized (spayed) female dogs with estrogen-responsive urinary incontinence. It is not intended for intact females, male dogs, or dogs whose incontinence has a different underlying cause, such as a urinary tract infection, bladder stones, or neurological condition. Your vet will typically rule out those possibilities before prescribing Incurin.
How Treatment Works in Practice
Treatment starts at 2 mg per day (two tablets), given orally once daily for at least 14 days. This initial period gives the drug enough time to build up its effect on the urethral tissues. Most owners notice a reduction in leaking during this phase.
Once the incontinence is under control, the goal is to find the lowest dose that still keeps the dog dry. The dose is reduced in steps: from 2 mg daily down to 1 mg daily, then to 0.5 mg daily, with at least seven days between each adjustment. If the dog remains continent on the lowest daily dose, the vet may try spacing it further to once every two days. The maximum dose is 2 mg per day.
This step-down approach matters because it minimizes the dog’s exposure to supplemental estrogen while still controlling symptoms. Some dogs do well on just half a tablet every other day. Others need the full 2 mg daily long-term. It varies by individual.
What to Expect Over Time
Incurin is typically a lifelong medication. Since the underlying cause is the permanent loss of ovarian estrogen, stopping the drug usually means the incontinence returns. Most dogs tolerate it well on an ongoing basis, especially once the dose has been reduced to the minimum effective level.
The medication is given by mouth and can be mixed with food. Because it’s a small tablet that can be halved, adjusting the dose is straightforward. You’ll likely have periodic veterinary check-ups to confirm the current dose is still working and to watch for any changes in your dog’s health.
Possible Side Effects
Because estriol is a mild estrogen, side effects tend to reflect its hormonal activity. Some dogs develop vulvar swelling, which mimics the appearance of a dog in heat. Increased attractiveness to male dogs can also occur for the same reason. Breast tissue enlargement is another possible effect. These signs are more common at higher doses and often resolve or lessen once the dose is reduced.
Gastrointestinal effects like decreased appetite or vomiting can occur but are generally uncommon. If you notice any of these changes, they’re worth reporting to your vet, as they may signal the dose can be lowered.
How Incurin Compares to Other Options
Before Incurin became available, the most common treatment for spay incontinence was phenylpropanolamine (PPA), a drug that works differently. PPA tightens the urethral sphincter by stimulating certain receptors in the muscle itself, rather than replacing estrogen. It remains widely used and is effective for many dogs.
Interestingly, research has shown that combining estriol with PPA does not increase urethral resistance beyond what estriol achieves alone. This suggests the two drugs work through overlapping pathways rather than complementary ones, so adding PPA on top of Incurin may not provide additional benefit. For dogs that don’t respond to one, switching to the other is a more common strategy than combining them.
The choice between the two often comes down to how a dog responds individually and whether side effects are a concern. PPA can raise heart rate and blood pressure, making it less ideal for dogs with certain cardiac conditions. Incurin’s hormonal side effects, while different in character, are generally mild and dose-dependent.