Adequan for Horses: How Often, Side Effects, the Recall, and What the Evidence Shows

What Adequan Is

Polysulfated glycosaminoglycan, given as a shot in the muscle.

Adequan i.m. is the brand name for polysulfated glycosaminoglycan, or PSGAG. Chemically, it resembles the glycosaminoglycans that make up the cushioning matrix of joint cartilage. The idea is that, once injected, it travels to inflamed joints, slows the enzymes that break cartilage down, and supports joint fluid. The manufacturer reports that after one shot, levels in joint fluid peak within about two hours and hyaluronic acid in the joint roughly doubles by 48 hours, while noting that the clinical significance of that increase is unknown.

The facts every owner should know:

• Dose: 500 mg intramuscularly every 4 days for 28 days, seven injections in all. The manufacturer calls it the "1, 4, 7" schedule.
• Labeled use: non-infectious degenerative or traumatic joint dysfunction and associated lameness of the carpal (knee) and hock joints.
• Route: intramuscular only. The label says plainly that it is not for injection into the joint.
• Prescription-only, and not for horses intended for human consumption. Safety has not been evaluated in breeding horses or pregnant or lactating mares.
• No generic. The manufacturer stresses that similarly named supplements and devices are not equivalent and are not FDA-approved.

Does Adequan Work?

It is safe and widely trusted. The controlled evidence is more modest than its reputation.

What the FDA approval was based on

The FDA's Freedom of Information summary for Adequan i.m., approved in November 1989, lists three efficacy studies. The first was a dose-finding study in 36 horses with arthritis deliberately induced in the knee, six horses per group. The 500 mg dose beat lower doses on joint flexion and stride after exercise, which is where today's dose comes from. The second was a 43-horse field trial comparing Adequan injected into the muscle with Adequan injected into the joint. There was no placebo group, and the two routes did not differ (overall P = 0.68). The third was an uncontrolled open trial of 42 cases, in which investigators rated 81% of results excellent or good.

That was a normal approval package for a drug of its era. But it means the approval does not include a placebo-controlled trial in horses with naturally occurring arthritis, the kind of horse most owners are treating.

What independent researchers found

Several university groups have tested intramuscular PSGAG against a control since then:

• Colorado State, 1989. Eight horses had cartilage defects created surgically in one knee and chemical damage in the other, then got 500 mg every 4 days for seven doses, the Adequan schedule. The authors concluded it had no effect on healing of the cartilage lesions and only minimal protective effect against the chemical damage.
• Cornell, 1993. In 21 ponies whose knees were injected with the corticosteroid methylprednisolone, PSGAG given in the muscle did not protect the cartilage against the steroid's loss of proteoglycan.
• Colorado State, 2009. In 24 horses with arthritis created in the standard surgical model, PSGAG in the muscle was used as the established comparison treatment. Shock wave therapy improved lameness significantly more than either placebo or PSGAG, and the researchers found no disease-modifying effect in joint fluid, joint lining or cartilage from the PSGAG horses.
• A 2010 study in 12 horses with chemically induced knee arthritis did find less lameness, less swelling and better flexion than saline, using a different PSGAG product given on the same every-4-days schedule.

On the other side of the ledger, a 2025 review in the Open Veterinary Journal concludes that PSGAG reduces clinical signs and qualifies as a disease-modifying osteoarthritis drug. You should know that its author was previously employed by the manufacturer as a researcher, and that the manufacturer funded the review. We tell you that for the same reason we tell you HempMy Pet funded the research on our own oil: who paid for a study matters when you are deciding how much weight to give it.

And there is the real world. In a 1996 survey of 1,522 equine practitioners, 90.5% used PSGAG and rated it moderately effective, with racehorse vets rating it highest and pleasure-horse vets lowest. That experience counts for something. It is just not the same thing as a controlled trial.

The honest bottom line: Adequan is about as safe as joint medications get, and it may help some horses, particularly with early or active joint inflammation. Go in expecting a modest, uncertain benefit rather than cartilage repair, and judge it on your own horse.

How Often to Give Adequan

The label says one thing. Barns do another.

The only FDA-approved regimen is the 1-4-7 series: one 500 mg injection every 4 days for seven doses. The manufacturer says you may repeat the full series if signs of arthritis return, at your vet's discretion, and its own FAQ states there is no approved maintenance, prophylactic or loading regimen.

In practice many horses get a "maintenance" shot every two to four weeks after the first series, often indefinitely. That is a legitimate extra-label choice your vet can make, and the safety data are reassuring: in the label's safety study, horses got up to 2,500 mg twice a week for 12 weeks, five times the dose and three times the duration, with no toxicity. What is missing is evidence that maintenance dosing keeps working. We could not find a published controlled study of any maintenance schedule in horses. If you go that route, agree with your vet on how you will tell whether it is earning its place.

How fast should you see a difference? In the manufacturer's dose study, carpal flexion improved by an average of 19% after four injections and 71% after all seven, in horses with induced arthritis. Plan to judge it after the full series, not the first few shots.

Side Effects and Safety

This is where Adequan genuinely shines.

Why Was Adequan Recalled?

One of the most-searched Adequan questions right now.

On 31 July 2026, American Regent recalled four lots after glass fibers were found while testing retained samples. For horses, the affected product is Adequan i.m. 500 mg/5 mL single-dose vials, lots 24416 and 25265P. Two Adequan Canine lots were also recalled. The company warned that injecting particles could cause pain, irritation, swelling, inflammation, infection or abscess at the injection site, and said it had received no reports of adverse events. Check the lot number on every box and vial in your barn, and talk to your vet or supplier about replacing affected stock.

Adequan vs Legend vs Pentosan vs Joint Injections

They are not interchangeable, and your vet may use more than one.

One difference worth knowing: Zycosan's approval came with a saline-controlled field study in client-owned horses with naturally occurring arthritis, the trial Adequan's approval package lacked. Its label also notes injection-site reactions and prolonged clotting times (aPTT and PT), with no bleeding seen in any horse.

How to Use Adequan Well: A Practical Protocol

Your vet sets the plan. These steps make it more likely you will know whether it worked.

1. Get a diagnosis. Know which joint and why. Adequan is labeled for non-infectious joint problems, and an infected joint is an emergency, not an Adequan case.
2. Record a baseline before the first shot. Film your horse trotting straight away, toward you and on a circle, on a firm surface. Ask your vet for flexion results. Without a before, you cannot judge an after.
3. Give the full series on schedule. 500 mg every 4 days for seven doses. Put the dates in your phone.
4. Prep the site like it matters. Clean thoroughly, use a fresh needle and never mix Adequan with anything else in the syringe.
5. Rotate injection sites and check each one over the next few days for heat or swelling.
6. Check the lot numbers against the July 2026 recall before you start.
7. Re-film after the series and compare side by side with your baseline.
8. Decide on maintenance deliberately. If you continue beyond the label, agree on the interval, the cost and the date you will reassess.
9. Combine, don't rely. Adequan works best as one part of a plan that includes weight, turnout, footing, hoof care and whatever else your vet recommends.
10. Check competition rules for your organization before show season, as you would for any medication.

When to Call Your Vet

• Heat, swelling or pain at an injection site that is getting worse, or lasts more than a couple of days
• Any sign of an abscess: a hot, painful swelling that may drain
• Hives, facial swelling or changes in breathing after a shot (call immediately)
• Lameness that gets worse during the series
• A sudden hot, swollen, very painful joint, which could mean infection
• No visible improvement after the full seven-dose series

What About Hemp?

Owners reaching for Adequan are usually managing a horse's joints for the long haul. So are most of the horse owners who ask us about hemp.

Hemp is not a replacement for Adequan or any treatment your vet prescribes. It has no role in an acute injury, a fresh lameness, an infected joint or anything undiagnosed.

Where it has a real, early evidence base is alongside conventional care for chronic joint stiffness. In a 2024 University of Messina study, 24 horses with mild osteoarthritis got an NSAID for five days, and half also got CBD in hemp oil for 14 days. By day 14 the median pain score was 3 in the CBD group against 7, scored by observers who did not know which horses got CBD. The caveats: the conventional drug in that study was bute, not Adequan, the control horses got no placebo oil, and it was a small, short study. We cover it fully in our bute guide.

Can you give CBD with Adequan?

No study has tested CBD and PSGAG together in horses. The manufacturer lists no known contraindications for Adequan beyond hypersensitivity, but its studies were run without other products. CBD itself is processed by the liver, and in a Colorado State study at higher doses, liver enzymes rose in 8 of 12 horses, all of which improved or normalized within 10 days of stopping. Tell your vet before combining them.

The rule for show horses

CBD is prohibited under USEF, FEI and HISA rules, with no validated withdrawal time. If your horse competes, hemp is off the table during the season. Our guide to CBD safety and show rules has the detail.

How owners actually use it: as a daily top-dress on feed for a retired or pleasure horse with long-term stiffness, started low and judged over two to four weeks, with the vet in the loop. Our horse dosing guide by body weight has the numbers, and our equine study page explains what Tarleton State did and did not find with our own oil.

Alternatives and Partners to Adequan

• Other approved systemic options: Legend (intravenous hyaluronic acid) and Zycosan (pentosan polysulfate in the muscle).
• Joint injections: corticosteroids, hyaluronic acid or biologics such as PRP and IRAP, chosen for the specific joint.
• Anti-inflammatories: bute or Equioxx for flare-ups. See our Equioxx guide for what long-term use involves.
• Management: daily turnout and steady movement, good footing, correct trimming or shoeing, and keeping the horse lean.
• Supplements: glucosamine, chondroitin, hyaluronic acid, omega-3s and hemp. Check competition rules first.

Questions to Ask Your Vet

• Which joint is the problem, and is it the kind of case Adequan suits?
• How will we measure whether it worked: flexion, video, a lameness score?
• After the first series, do you recommend maintenance? At what interval, and when do we reassess?
• Would Zycosan, Legend or a joint injection be a better fit for this horse?
• Are any of my vials from the July 2026 recall lots?
• If I want to add hemp oil for chronic stiffness, is there any reason it would not suit this horse?

Frequently Asked Questions

What are the negative side effects of Adequan?
Very few. No adverse reactions were recorded in the FDA field trials or the horse safety study, where horses got five times the dose for three times as long without toxicity. The realistic risks are local: soreness, swelling or, with poor technique, infection at the injection site. It is labeled for intramuscular use only, not for injection into joints, and hypersensitivity is the only listed contraindication. Safety has not been evaluated in breeding, pregnant or lactating horses.

What are the pros and cons of Adequan for horses?
The pros are an excellent safety record, FDA approval, easy intramuscular dosing and wide acceptance among equine vets. The cons are cost, a seven-shot series, and modest controlled evidence: its approval rested on an induced-arthritis study, a field trial with no placebo group and an uncontrolled trial, and three of four independent controlled studies found intramuscular PSGAG did not beat the control. There is also no approved maintenance schedule.

How often do you give Adequan to a horse?
The FDA-approved regimen is 500 mg intramuscularly every 4 days for 28 days, seven injections. The manufacturer says the full series can be repeated when signs of arthritis return. Many vets also prescribe maintenance injections every two to four weeks, which is an extra-label choice; the safety data are reassuring, but no published controlled study shows that maintenance dosing keeps working.

Why is Adequan being recalled?
On 31 July 2026, American Regent recalled four lots after glass fibers were found in retained samples. The equine lots are Adequan i.m. 500 mg single-dose vials, lots 24416 and 25265P; two Adequan Canine lots were also included. The company warned of possible injection-site pain, swelling, infection or abscess, and reported no adverse events at the time. Check the lot number on every vial you have.

How long does it take to see results from Adequan in horses?
Judge it after the full seven-dose series, about four weeks. In the manufacturer's dose study in horses with induced arthritis, carpal flexion improved an average of 19% after four injections and 71% after seven. Filming your horse trotting before the first injection and after the last is the simplest way to see a real difference.

What is a good alternative to Adequan for horses?
Approved systemic alternatives include Zycosan (pentosan polysulfate, given in the muscle weekly for four doses) and Legend (intravenous hyaluronic acid). Joint injections of corticosteroids, hyaluronic acid or biologics such as PRP and IRAP target a specific joint. Management, including turnout, footing, hoof care and weight control, matters for every arthritic horse, and supplements such as omega-3s and hemp oil can support long-term comfort.

What is the most effective injection for treating arthritis in horses?
There is no single answer; it depends on the joint, how advanced the arthritis is and the horse's job. Direct joint injections of corticosteroids, often combined with hyaluronic acid, are widely used for targeted relief, while systemic options like Adequan, Zycosan and Legend treat more broadly. Your vet will usually combine approaches.

Can you give CBD with Adequan?
Tell your vet first. No study has tested CBD and PSGAG together in horses. Adequan has no known contraindications beyond hypersensitivity, while CBD is processed by the liver and raised liver enzymes in 8 of 12 horses at higher doses in one study, all of which normalized after stopping. CBD is prohibited for horses competing under USEF, FEI and HISA rules.

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These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease. This article is general information, not veterinary advice. Never start, stop or change your horse's prescription without your veterinarian.