Adequan is an FDA-approved injectable drug used to treat joint disease in horses. Its active ingredient is polysulfated glycosaminoglycan (PSGAG), a compound derived from animal cartilage that works directly on damaged joints to slow cartilage breakdown and reduce lameness. It is the only FDA-approved intramuscular joint therapy for horses and has become one of the most widely used treatments in equine sports medicine.
What Adequan Is Approved to Treat
Adequan i.m. is specifically approved for the intramuscular treatment of non-infectious degenerative and traumatic joint dysfunction and associated lameness of the carpal (knee) and hock joints in horses. In plain terms, that means it targets arthritis and joint damage caused by wear, tear, and injury rather than infection. Many veterinarians also use it off-label for joint problems in other locations, but the formal approval covers those two joints.
How It Works Inside the Joint
Adequan does three things at the joint level, which is what sets it apart from simple pain relievers.
First, it blocks the destructive enzymes that break down cartilage and joint fluid. Joints affected by arthritis produce elevated levels of enzymes that chew through cartilage proteins, the elastic fibers that give cartilage its cushion, and hyaluronic acid (the thick, lubricating substance in joint fluid). PSGAG inhibits a broad range of these enzymes at very low concentrations. For some of these enzymes, the drug essentially acts as a decoy, getting attacked instead of the cartilage. For others, it physically binds to the enzyme and deactivates it. In lab studies using equine joint cells, PSGAG was the only drug able to significantly inhibit one key cartilage-destroying enzyme at concentrations that realistically occur in a horse’s joint after injection.
Second, it stimulates the cells in cartilage and the joint lining to produce new cartilage components and fresh hyaluronic acid. Studies in horses, pigs, and humans have all shown increased hyaluronic acid concentration in joint fluid after PSGAG therapy. The hyaluronic acid produced tends to be higher in molecular weight, which means it’s better at lubricating and cushioning the joint.
Third, the drug binds directly to damaged cartilage matrix, where it may improve the tissue’s ability to hold water and protect what’s left from further enzymatic breakdown. Healthy cartilage acts like a sponge that absorbs shock; when it loses water-binding capacity, it becomes brittle and vulnerable. PSGAG appears to partially restore that function.
Dosing and Administration
The FDA-approved protocol is straightforward: one 500 mg intramuscular injection every 4 days for a total of 7 injections, spanning 28 days. Veterinarians and the manufacturer often refer to this as “one, four, seven” dosing. The injection goes into a large muscle, typically the hindquarters, rather than directly into the joint.
After the initial series, the interval for retreatment is at the veterinarian’s discretion. There is no standardized maintenance schedule on the label. Instead, the recommendation is to monitor the horse for returning signs of stiffness or lameness and repeat the full seven-injection series when clinical signs come back. Some veterinarians prescribe periodic single injections as maintenance between full courses, though this is off-label.
Side Effects and Safety Concerns
Adequan is generally well tolerated. The most commonly reported adverse reaction is a mild, temporary soreness at the injection site, and even that is rare.
The more important safety considerations involve the drug’s blood-thinning properties. PSGAG has anticoagulant effects, meaning it can slow blood clotting. Because of this:
- Bleeding disorders: Horses with any known tendency toward hemorrhage or prolonged clotting times should not receive Adequan.
- Post-surgery timing: The drug should not be given within 24 hours after surgery.
- Drug interactions: Using Adequan alongside blood thinners increases the risk of hemorrhage. Combining it with NSAIDs (common anti-inflammatory painkillers like phenylbutazone) increases the risk of gastrointestinal bleeding specifically.
- Overdose: If too much is given, clotting time can be prolonged for about 8 hours after injection.
Adequan is also contraindicated in horses with advanced kidney or liver disease, in pregnant or lactating mares, and in cases of septic (infected) arthritis, which requires antibiotics or surgery rather than a joint-protective drug.
Adequan vs. Legend
The two most common injectable joint therapies in equine practice are Adequan and Legend (hyaluronate sodium). They work differently and are given differently, so they’re not interchangeable.
Legend is an intravenous injection of hyaluronic acid, given once a week for three weeks and then typically once a month. It works primarily on the synovial lining of the joint, stimulating the body to produce more of its own hyaluronic acid and reducing the production of inflammatory compounds that destroy cartilage. Its main effect is improving joint lubrication and dampening inflammation.
Adequan is an intramuscular injection that targets cartilage more directly, blocking the enzymes that degrade it while also stimulating new cartilage and joint fluid production. Because the two drugs act on different parts of the joint disease process, some veterinarians use both in combination for horses with significant arthritis. Adequan addresses the cartilage breakdown side of the equation, while Legend focuses on joint fluid quality and inflammation at the synovial membrane.
What to Expect During Treatment
Most horse owners notice improvement gradually over the course of the 28-day initial series rather than after a single injection. The drug is not a painkiller, so it won’t produce the immediate relief you’d see from an anti-inflammatory. Instead, it works by changing the chemical environment inside the joint over time, slowing destruction and encouraging repair. Some horses show noticeable improvement in comfort and movement by the third or fourth injection.
Because Adequan addresses the underlying joint disease rather than masking pain, it’s often used as part of a broader management plan that includes controlled exercise, proper footing, farrier care, and sometimes additional therapies. It does not regenerate cartilage that has already been completely lost, so earlier intervention tends to produce better outcomes than waiting until joint disease is advanced.