Hyaluronic Acid for Horses: Benefits, Uses & Side Effects

This information is for educational purposes only. Never give your pet any medication without your veterinarian's guidance. Dosing, frequency, and safety depend on your pet's specific health profile.

Hyaluronic acid, also called hyaluronan or hyaluronate sodium, is a naturally occurring substance found in normal joint fluid and cartilage. In horses, it is used as a prescription joint medication to support the lubricating and shock-absorbing qualities of synovial fluid when a joint is inflamed. Your vet may use an FDA-approved injectable product such as Legend, or another veterinary-labeled formulation, depending on the joint involved and the treatment plan.

In practical terms, hyaluronic acid is most often used when a horse has non-infectious synovitis or early osteoarthritis. These conditions can reduce the normal thickness and elasticity of joint fluid. Replacing or supplementing hyaluronic acid may help improve joint lubrication, reduce inflammatory mediators, and ease lameness in some horses.

This medication is not a cure for every cause of lameness. It works best when your vet first identifies which joint is painful and why. Horses with fractures, advanced joint damage, or septic arthritis usually need a broader plan than hyaluronic acid alone.

Hyaluronic acid is mainly used for joint dysfunction caused by non-infectious synovitis associated with equine osteoarthritis, especially in the carpus (knee) and fetlock. Your vet may recommend it when a horse is stiff, short-strided, or mildly lame after work, and diagnostics suggest inflammation inside the joint rather than infection.

It is commonly used in two ways: intravenously (IV) or intra-articularly (directly into the joint). Intra-articular treatment is often chosen when one specific joint is the problem. IV treatment may be considered when your vet wants a less invasive option or when direct joint injection is not ideal that day.

Some horses receive hyaluronic acid as part of a larger lameness plan that may also include rest, controlled exercise, corrective farriery, rehabilitation, NSAIDs, or corticosteroid joint therapy. Oral supplements containing hyaluronic acid are also marketed for maintenance, but injectable forms generally have stronger evidence for active joint inflammation.

Hyaluronic acid dosing in horses depends on the product, route, joint involved, and your horse's diagnosis. For FDA-approved Legend, label information supports 40 mg (4 mL) IV once weekly for 3 treatments for intravenous use, while certain formulations are labeled for intra-articular use in the carpus or fetlock at lower per-joint volumes. Because products are not interchangeable vial-for-vial, your vet should choose the exact dose and route.

Intra-articular injections must be performed using sterile technique by your veterinary team. That matters because any joint injection carries a small but serious risk of introducing infection. After treatment, your vet may recommend a short period of reduced exercise, hand-walking, or a gradual return to work.

Do not try to estimate a dose from another horse's prescription. A horse with mild fetlock synovitis, a horse with multiple affected joints, and a horse with advanced osteoarthritis may all need different plans. Your vet may also adjust timing based on response, imaging findings, competition schedule, and whether other joint medications are being used at the same visit.

Most horses tolerate hyaluronic acid well, and reported adverse effects are usually uncommon and mild. That said, side effects can still happen. After an intra-articular injection, some horses develop a temporary joint flare with heat, swelling, or increased soreness for a day or two. This is inflammatory, not always infectious, but it still deserves a call to your vet.

A more serious concern is joint infection (septic arthritis) after injection. This is uncommon, but it is an emergency. Call your vet right away if your horse becomes suddenly much more lame, the joint becomes very hot or swollen, or your horse develops fever, marked pain, or reluctance to bear weight.

With IV administration, reactions are uncommon, but any injectable medication can potentially cause local irritation or hypersensitivity. Product labeling also notes that safety has not been fully established in breeding stallions or in breeding, pregnant, or lactating mares for some formulations. If your horse fits one of those categories, ask your vet whether another option makes more sense.

Hyaluronic acid is often used alongside other joint therapies rather than instead of them. In equine practice, your vet may pair it with corticosteroids during a joint injection visit, or use it as part of a plan that also includes NSAIDs such as phenylbutazone or firocoxib. That does not automatically mean there is a harmful interaction, but it does mean the full treatment plan should be coordinated carefully.

The biggest practical concern is not a classic drug-drug interaction. It is whether combining medications could mask worsening disease, increase procedure frequency, or complicate interpretation of your horse's response. If your horse is receiving repeated joint injections, systemic anti-inflammatories, biologics, or supplements, your vet should know about all of them.

Tell your vet about every prescription, supplement, and show medication your horse receives. That includes oral joint products, corticosteroid injections, NSAIDs, and any competition-related withdrawal concerns. If your horse has a history of joint infection, bleeding problems, or a reaction after previous injections, mention that before the next dose.