Proin is an FDA-approved medication used to treat urinary incontinence in dogs. It contains phenylpropanolamine, a drug that tightens the muscles controlling the bladder outlet, helping dogs that leak urine involuntarily. The condition it targets, urethral sphincter mechanism incompetence (USMI), is especially common in spayed female dogs, though it can affect any dog.
How Proin Works
The muscle that keeps the bladder closed between bathroom trips can weaken over time, particularly after spaying. When this muscle loses tone, urine leaks out during sleep, rest, or excitement. Proin works by triggering the release of a chemical messenger called norepinephrine, which causes that sphincter muscle to contract more tightly. It also slows the breakdown of norepinephrine at the site, prolonging the tightening effect. The result is a stronger seal at the bladder outlet, which reduces or stops leaking.
The standard dose is given twice daily for the regular chewable tablet version. An extended-release formulation (Proin ER) is also available, designed for once-daily dosing. Your vet will determine the right tablet size based on your dog’s weight.
What Incontinence Looks Like
Dogs with USMI don’t squat and urinate inappropriately. Instead, they leak without realizing it. You might notice wet spots where your dog was sleeping, damp fur around the back legs, or a urine smell on bedding. It’s not a behavioral issue, and dogs can’t control it. This type of incontinence is distinct from house-training problems or urinary tract infections, both of which involve conscious urination in the wrong place or at the wrong time.
Medium to large breed spayed females are most commonly affected, often developing the problem months to years after their spay surgery. The drop in estrogen after spaying is thought to contribute to the gradual weakening of the urethral sphincter, though the exact relationship is still debated.
Common Side Effects
Proin is effective for most dogs, but it comes with a meaningful side effect profile. In a 28-day clinical study of 123 dogs on Proin, the most frequently reported issues were:
- Vomiting: 20.3% of treated dogs, compared to 8.2% on placebo
- High blood pressure: 19.5% of treated dogs developed readings at or above 160 mmHg
- Loss of appetite: 16.3%, versus 3.3% on placebo
- Weight loss greater than 5%: 16.1% of treated dogs
- Anxiety, aggression, or behavior changes: 9.7%, versus 3.2% on placebo
- Lethargy: 5.7%
- Sleep problems: 2.5%, not seen in the placebo group
These numbers climbed in a longer six-month study. High blood pressure appeared in 34.6% of dogs, and weight loss greater than 5% affected nearly a quarter of them. The appetite suppression and restlessness make sense pharmacologically: Proin stimulates the same type of receptors that the body’s “fight or flight” system uses, so it can rev up the cardiovascular system and make dogs feel jittery or on edge.
Post-approval reports, which capture rarer events from widespread use, have also documented panting, tremors, seizures, and in uncommon cases, sudden death sometimes preceded by neurological signs or collapse. One necropsy revealed bleeding in the brain. These serious outcomes are rare but worth understanding, especially for dogs on long-term therapy.
Dogs That Shouldn’t Take Proin
Because Proin raises blood pressure, it should be used cautiously (or not at all) in dogs with pre-existing heart disease, high blood pressure, kidney insufficiency, liver disease, diabetes, or glaucoma. All of these conditions either worsen with elevated blood pressure or make the cardiovascular effects of the drug more dangerous.
Proin also interacts with several other medications. Dogs taking tricyclic antidepressants or monoamine oxidase inhibitors (like selegiline, sold as Anipryl for canine cognitive dysfunction) face a risk of unpredictable and potentially dangerous blood pressure swings. Other stimulant-type drugs can amplify Proin’s effects as well. If your dog takes any ongoing medication, your vet needs to know before starting Proin.
What to Watch for at Home
The most practical things to monitor are your dog’s behavior, appetite, and weight. Restlessness, irritability, or unusual aggression can signal that the drug is overstimulating your dog’s nervous system. A dog that stops eating or drops weight steadily may need a dose adjustment or a different treatment approach. Worsening incontinence despite treatment is also a reason to check back in with your vet, since it could indicate a different underlying problem.
Because high blood pressure is the most common clinical concern and tends to increase with longer use, periodic blood pressure checks are a reasonable part of ongoing care. Blood pressure problems in dogs don’t produce obvious outward signs until they’re severe, so you can’t rely on watching your dog’s behavior alone to catch them. Dogs on Proin long-term benefit from regular veterinary checkups that include cardiovascular monitoring.
Alternatives to Proin
Proin isn’t the only option for canine incontinence. Estrogen-based therapies are sometimes used, particularly in spayed females, to help restore urethral tone through a different pathway. Some dogs respond well to a combination approach. In cases where medication doesn’t work or isn’t tolerated, surgical options exist, including procedures that physically support the urethra. Your vet can help weigh the tradeoffs based on your dog’s health history and how well they tolerate medication.