Solensia is a monthly injection for cats that relieves osteoarthritis pain by neutralizing a specific pain-signaling protein called nerve growth factor (NGF). Unlike traditional painkillers that block pain after it reaches the nervous system, Solensia intercepts the process earlier, preventing pain signals from being amplified at their source in the joints.
The Pain Pathway Solensia Targets
Nerve growth factor plays a central role in how pain sensors become hypersensitive during both acute and chronic pain, including osteoarthritis. In a healthy joint, NGF helps regulate nerve function. But in an arthritic joint, NGF levels spike, and those elevated levels essentially turn up the volume on pain receptors. Nerves in and around the joint become increasingly sensitive, so even normal movement starts to register as painful. Over time, this sensitization can make a cat reluctant to jump, climb stairs, or even shift positions while resting.
Solensia’s active ingredient, frunevetmab, is a monoclonal antibody designed specifically for cats. It works by binding to NGF molecules in the bloodstream and joint tissues, essentially trapping them before they can attach to nerve receptors. With NGF sequestered and unable to interact with those receptors, the pain-sensing nerves gradually dial back their sensitivity. The joint damage itself doesn’t change, but the cat’s experience of pain from that damage does.
Why a “Felinized” Antibody Matters
Monoclonal antibodies are lab-made proteins that mimic the immune system’s natural ability to target specific molecules. Solensia is described as “felinized,” meaning it was engineered to closely resemble a cat’s own antibodies. This matters because a cat’s immune system is less likely to recognize the drug as foreign and mount a reaction against it. It also allows the antibody to circulate in the body longer, which is why a single injection can last about a month.
This is the same general approach used in many human medications for conditions like migraines and certain cancers, adapted here for feline biology. Solensia was the first monoclonal antibody approved by the FDA for use in any animal for pain control.
How Quickly It Works
Some cats show noticeable improvement within two weeks of the first injection, but a full response often takes longer. Clinical response can be delayed six to eight weeks, which is when the drug reaches steady-state concentrations in the body. This means the first injection or two may seem underwhelming. Veterinarians typically recommend committing to at least two or three monthly injections before judging whether Solensia is helping your cat.
In a multisite clinical trial, about 80% of cats receiving Solensia were considered treatment successes by day 56 (roughly two months), compared to about 45% of cats receiving a placebo. The difference between the treatment and placebo groups became statistically significant around the six-week mark, reinforcing that patience with the first few doses is important. Improvements owners typically notice include more willingness to jump, increased activity, smoother movement, and less apparent stiffness.
How It’s Given
Solensia is administered as a subcutaneous injection, meaning it goes just under the skin, similar to a vaccine. Your veterinarian gives it in the clinic once a month. It is not available for at-home administration. The injection itself is small-volume and generally well tolerated, with most cats barely reacting to the needle.
The drug is approved for cats only. A similar product called Librela (bedinvetmab) exists for dogs, targeting the same NGF pathway but engineered for canine biology.
Reported Side Effects
No drug is without risks, and Solensia has generated a substantial number of adverse event reports since its approval in early 2022. The most commonly reported issues in FDA post-market surveillance include skin-related reactions (scabbing, itching, hair loss, and dermatitis), vomiting, lethargy, diarrhea, and decreased appetite. Some cats develop itching specifically around the face and head.
It’s worth noting that these are spontaneous reports from veterinarians and pet owners, not controlled trial data, so they can’t be used to calculate how common any given side effect actually is. Many cats receive Solensia without any noticeable problems. Still, the skin-related reports are frequent enough that they deserve attention. If your cat develops new itching, scabbing, or hair loss after starting Solensia, that’s worth discussing with your vet before the next dose.
Which Cats Shouldn’t Receive It
Solensia is contraindicated in breeding cats and in pregnant or lactating queens. The antibody can cross the placental barrier and pass into milk. Studies in rodents and primates given anti-NGF antibodies showed fetal abnormalities, increased stillbirths, and higher rates of newborn death. Cats with a known hypersensitivity to frunevetmab should also not receive additional doses.
For cats with kidney disease, which is extremely common in older cats who also tend to have arthritis, Solensia has a potential advantage over traditional anti-inflammatory painkillers. Standard anti-inflammatory drugs can be hard on the kidneys, and many are not approved for long-term use in cats at all. Because Solensia works through a completely different mechanism, targeting a single protein rather than broadly suppressing inflammation, it doesn’t carry the same kidney-related concerns. This is one of the main reasons it filled such a gap in feline pain management when it launched.
How It Compares to Traditional Pain Relief
Before Solensia, options for managing chronic arthritis pain in cats were limited. Cats metabolize many common painkillers poorly, making long-term use of most oral anti-inflammatory drugs risky. Gabapentin and buprenorphine were sometimes used, but each comes with sedation or other trade-offs that make them imperfect for daily, long-term management.
Solensia’s monthly injection schedule also sidesteps one of the biggest practical challenges in feline medicine: giving a cat oral medication every day. Many cat owners know the difficulty of pilling a cat, and compliance with daily medication drops off quickly. A single monthly vet visit removes that variable entirely, which in practice means more cats actually receive consistent pain management over time.