Incurin typically takes about 14 days to produce noticeable improvement in urinary incontinence. In the FDA clinical trial, 66% of dogs achieved treatment success by day 14 on the standard starting dose. After that initial two-week period, your vet may spend several more weeks fine-tuning the dose, so the full process of finding the right amount for your dog can take up to six weeks.
What Happens in the First Two Weeks
Incurin contains estriol, a mild estrogen that works by strengthening the muscles that keep the bladder closed. In spayed female dogs, the drop in natural estrogen after surgery can weaken the urethral seal over time, leading to urine leaks, especially during sleep or relaxation. Estriol binds to estrogen receptors in the lower urinary tract, increasing the functional length of the urethra and raising the pressure threshold the bladder needs to reach before releasing urine. This doesn’t happen overnight because the tissue needs time to respond to the restored hormone signaling.
During the clinical trial, dogs received 2 mg once daily for the first 14 days. By the end of that period, about two-thirds of treated dogs showed meaningful improvement compared to roughly one-third on placebo. So while two weeks is the benchmark for seeing results, about one in three dogs may not respond at the starting dose within that window.
The Dose Adjustment Phase
If your dog is responding well after two weeks, your vet will likely try to lower the dose. The goal is to find the smallest effective amount. In the clinical trial, vets were allowed to adjust the dose up or down at weekly intervals from day 21 through day 42. This means the full timeline from first pill to settled maintenance dose is roughly four to six weeks.
During this period, you’re essentially the observer. Keep track of how often leaks happen, whether they occur during sleep or while your dog is awake, and any changes in the size of wet spots. That information helps your vet decide whether to hold the dose steady, reduce it, or bump it back up.
How Incurin Compares to Proin
The other common medication for canine incontinence, phenylpropanolamine (sold as Proin), works through a completely different mechanism. It directly tightens the urethral muscle by stimulating certain receptors in the nervous system, reaching peak blood levels within about two hours of a dose. That means Proin can produce noticeable effects within a day or two, much faster than Incurin’s two-week timeline.
The tradeoff is that Proin’s effects wear off quickly (its half-life is only three to four hours for the standard formulation), so missed doses are more immediately noticeable. Incurin works more gradually but produces a sustained change in the tissue itself, which is why the effects build over days rather than hours. Some dogs end up on one or the other, and in stubborn cases vets may use both, though your vet will guide that decision based on your dog’s health profile.
Side Effects to Watch For
Because Incurin is a hormone, the most common side effects fall into two categories: digestive upset and estrogen-related changes. In clinical trials, the most frequently reported issues were:
- Loss of appetite: 13% of dogs, compared to about 4% on placebo
- Vomiting: about 10% of dogs
- Swollen vulva: about 4% of dogs (this did not occur in the placebo group)
- Attracting male dogs: about 3.5%, because the estrogen can mimic some signals of being in heat
- Increased thirst: about 7%, though this occurred at a similar rate in placebo-treated dogs
Less common but worth knowing about: during the dose adjustment phase, about 4% of dogs developed vulvar irritation or inflammation, and 4% showed lethargy. A small number showed behavioral changes like increased aggression or hyperactivity. Post-market data from several countries found that hair loss was the most commonly reported long-term side effect, accounting for roughly 20% of adverse reaction reports.
Rare but serious reactions reported over years of use include vaginal bleeding, blood cell count changes, and aggressive behavior severe enough to lead to euthanasia in three dogs after six months or more of treatment. These are uncommon, but they underscore why ongoing monitoring matters.
Monitoring While Your Dog Takes Incurin
Your vet should run baseline bloodwork and a urinalysis before starting Incurin. A complete blood count is recommended two to four weeks after starting the medication, then every three to six months for as long as your dog stays on it. This schedule exists because estrogens can, in rare cases, suppress bone marrow function, which would show up as changes in red blood cells, white blood cells, or platelets.
At home, the main things to watch for are the side effects listed above, particularly swelling of the vulva, appetite changes, vomiting, or any behavioral shifts. If you notice these, stop giving the medication and contact your vet rather than waiting for the next scheduled visit.
What If It Doesn’t Work
A 66% success rate at two weeks means a meaningful number of dogs don’t fully respond. If your dog still leaks after the full six-week trial with dose adjustments, that doesn’t necessarily mean the situation is hopeless. Some dogs respond better to phenylpropanolamine, and some do well on a combination of both medications. In cases where neither medication is sufficient, your vet may explore other options including injectable treatments that add bulk around the urethra, or surgical approaches. The underlying cause of the incontinence also matters: if it turns out to be something other than the typical post-spay sphincter weakness (like a urinary tract infection, bladder stones, or a structural problem), treating that root cause may resolve the leaking entirely.