Solensia is a monthly injection for cats that treats pain caused by osteoarthritis. It’s the first FDA-approved treatment specifically designed to control osteoarthritis pain in cats, filling a gap that existed for decades since most traditional pain relievers carry significant risks for felines. The active ingredient, frunevetmab, is a lab-made antibody that intercepts pain signals before they reach the brain.
How Solensia Works
Osteoarthritis pain in cats is driven largely by a protein called nerve growth factor, or NGF. When joints become inflamed, the body produces excess NGF, which binds to receptors on nerve cells and triggers a cascade that amplifies pain signals and makes nerves increasingly sensitive. Over time, this process means even normal joint movement starts to hurt.
Solensia is a “felinized” monoclonal antibody, meaning it was engineered to look like a natural cat antibody so the immune system doesn’t reject it. Once injected, it circulates through the bloodstream, finds NGF molecules, and binds to them. This prevents NGF from attaching to nerve receptors, effectively turning down the volume on pain signaling at its source. It doesn’t repair the joint or reverse arthritis. It blocks the pain pathway so your cat can move more comfortably.
What the Clinical Trials Showed
In the FDA’s pivotal studies, cats were assessed by their owners using a scoring system that tracked everyday activities like jumping, climbing, and playing. A cat counted as a treatment success if its overall score improved meaningfully without any single activity getting worse.
In the confirmatory trial, 75.1% of cats receiving Solensia were considered treatment successes by day 56, compared to 64.8% of cats receiving a placebo. By day 84 (after three monthly injections), the success rate climbed to 76.5% versus 67.3% for placebo. An earlier exploratory study showed a more dramatic separation: by day 56, 80% of treated cats improved compared to just 47.1% on placebo.
The placebo response in these studies was notably high, which is common in veterinary pain trials where owners are hoping for improvement and may interpret normal behavior fluctuations positively. Still, across both studies, the gap between Solensia and placebo widened with each monthly injection, suggesting the drug builds effectiveness over time. Many veterinarians recommend trying at least two or three doses before judging whether it’s working for your cat.
How It’s Given
Solensia is administered as a subcutaneous injection (under the skin) once a month at your veterinarian’s office. The dose is based on your cat’s body weight. It’s not a medication you give at home, so it requires a monthly vet visit. For cats that are stressed by car rides or clinic environments, this is worth factoring into your decision, though many owners find the visits become routine quickly.
Each injection lasts roughly four weeks. Some owners notice improvement within the first week or two, while others don’t see clear changes until after the second or third dose.
Possible Side Effects
The most commonly reported side effects involve the skin. Based on post-market adverse event reports collected by the FDA between January 2022 and June 2024, the most frequently reported reactions include skin scabs, itching (especially around the face and head), vomiting, lethargy, diarrhea, decreased appetite, hair loss, and dermatitis. Some cats develop localized reactions at the injection site, including scabbing or hair loss.
Skin reactions deserve particular attention because they appear across the reports in many forms: scabbing, itching, scratching, sores, redness, and in some cases bacterial skin infections. If your cat starts scratching excessively, developing crusty patches, or losing fur after starting Solensia, that’s something to report to your vet promptly. These reactions can range from mild and self-limiting to significant enough to discontinue treatment.
It’s important to note that these are voluntarily reported adverse events, not controlled study data. The FDA cautions that raw report numbers can’t be used to calculate how common side effects actually are, since there’s no way to know the total number of cats receiving the drug. Many cats tolerate Solensia well, but the pattern of skin-related complaints is consistent enough to watch for.
Which Cats Should Not Receive It
Solensia is contraindicated in cats with a known allergy to the drug and in breeding cats, pregnant queens, or nursing mothers, because the antibody can cross the placenta and pass into milk. It has not been evaluated in kittens younger than 7 months or cats weighing less than 5.5 pounds.
The safety of combining Solensia with NSAIDs (a class of common pain relievers) has not been established in cats, so these drugs generally shouldn’t be used together without veterinary guidance. The same applies to combining Solensia with other monoclonal antibody treatments. Long-term effects beyond six months of use have not been formally studied, which is relevant since osteoarthritis is a lifelong condition and many cats would need ongoing treatment.
Recognizing Osteoarthritis in Cats
One reason osteoarthritis is so underdiagnosed in cats is that cats hide pain exceptionally well. They don’t limp the way dogs do. Instead, the signs are behavioral: your cat stops jumping onto the bed, hesitates before climbing stairs, grooms less (or over-grooms painful joints), becomes less playful, or seems stiff when getting up from a nap. Some cats become irritable or withdraw socially.
Veterinarians may use owner questionnaires like the Feline Musculoskeletal Pain Index, developed at North Carolina State University, which asks you to rate your cat’s ability to perform specific activities. These tools help quantify subtle changes that you might otherwise chalk up to normal aging. Studies estimate that the majority of cats over age 12 have radiographic evidence of osteoarthritis, though not all of them show obvious signs of pain.
If your cat has slowed down and you’ve been assuming it’s just getting older, it’s worth asking your vet to evaluate for joint pain. Solensia won’t help every cat, but for those with genuine osteoarthritis pain, it offers a targeted option that avoids the kidney and gastrointestinal risks that make most traditional painkillers problematic for long-term use in cats.