Part 2: Dog joint supplements: Do they work?

In Part 1: What Glucosamine Bioavailability Research Actually Shows for Senior Dogs, I covered dog joint supplement bioavailability, and posed the question of whether oral glucosamine actually reaches a dog’s bloodstream.

The answer was yes, but….only a fraction. That answer leaves the more important question of, if only some glucosamine reaches the blood, does it actually help an arthritic dog move with less pain? That question is answered by a different kind of study, and it is the one this article takes on.

Here is the short version: The studies that make glucosamine look effective mostly compare it to prescription painkillers. They also measure improvement by eye and have no placebo group. The trials that actually compare dog joint supplements to a placebo, by measuring how much weight dogs put on their legs, find almost no improvement. Understanding these two kinds of studies, and why they disagree, are the two most useful lessons that senior dog owners can take away from this research.

The trials at a glance

Of the four glucosamine trials below, only one found a benefit…and this study also had no placebo group. The fifth study explains why that matters.

Study	Compared against	Dogs	Length	How improvement was measured	Result for glucosamine/chondroitin
Kampa et al. 2023	Placebo, carprofen, two marine oil products	75 analyzed	6 weeks	Force plate (weight bearing), vet exam	No significant improvement; carprofen and both marine oils did improve
Scott et al. 2017	Placebo	60	97 days	Activity monitor, owner questionnaire	No difference from placebo; owners reported improvement in both groups
Conzemius & Evans 2012	(placebo arm only)	58	Not a glucosamine trial	Force plate vs. owner and vet opinion	About 40% of owners saw improvement that the force plate did not
McCarthy et al. 2007	Carprofen (no placebo)	42 enrolled, 35 finished	70 days	Vet scoring by eye	Significant improvement by day 70
Moreau et al. 2003	Placebo, carprofen, meloxicam	71	60 days	Force plate, vet and owner opinion	No significant improvement; both NSAIDs did improve

Two ways to test a joint supplement

A clinical trial needs something to compare the supplement against, and that choice shapes the answer.

A placebo-controlled trial gives some dogs the supplement and others an identical-looking dummy. Nobody handling the dogs knows which is which. If the supplement group does better, the supplement is probably doing something.

An active-controlled trial compares the supplement to a treatment already known to work, usually an NSAID like carprofen (Rimadyl). If both groups improve, it is tempting to conclude the supplement works too. But that design has a blind spot. Arthritis symptoms wax and wane, owners and vets expect improvement, and dogs often enter a study on a bad stretch that would have eased anyway. Without a placebo group, none of that can be separated from a real effect.

McCarthy 2007: the study supplement makers lean on

McCarthy and colleagues ran the trial most often cited as proof that glucosamine works in dogs. It is a real, randomized, double-blind study, and it deserves a fair reading.

The researchers enrolled 42 client-owned dogs with chronic lameness and stiffness; 35 completed the study. Half received a glucosamine hydrochloride and chondroitin sulfate product, which also contained N-acetyl-D-glucosamine, vitamin C, and zinc. The other half received carprofen. Veterinarians scored pain, weight bearing, and overall severity on a visual scale over 70 days.

By day 70, the glucosamine group showed statistically significant improvement in all three scores. Carprofen worked faster.

Here is what the study can and can’t tell us:

• It shows that dogs on the supplement were scored as better at day 70 than at the start.
• It can’t show whether they improved because of the supplement. With no placebo group, ordinary ups and downs, the expectation of improvement, and a dog’s starting point all look the same as a treatment effect.
• It relied on judgment by eye. Vets scored the dogs subjectively. As we’ll see below, that is exactly where a placebo effect shows up in veterinary studies.

None of this means the researchers did anything wrong. Active-controlled designs are common and ethical, because they avoid leaving painful dogs untreated. It just means this study answers a narrower question than what product labels claim.

Moreau 2003: the trial with a placebo and a force plate

Four years earlier, Moreau and colleagues ran the comparison McCarthy didn’t. They randomly assigned 71 client-owned dogs with osteoarthritis to one of four groups: a glucosamine and chondroitin product, carprofen, meloxicam, or a placebo. The study was double-blind and ran 60 days.

What makes this study stand out is how it measured improvement. Along with owner and surgeon opinions, the dogs walked across a force plate, which is a floor sensor that records how much weight each leg actually carries. A dog in pain shifts weight off the sore limb, and the plate catches that shift.

The results:

• Carprofen and meloxicam both significantly improved weight bearing on the arthritic limb. Meloxicam brought it back to normal.
• The glucosamine product did not significantly improve weight bearing.
• The orthopedic surgeons judged that the two NSAIDs helped. The owners judged that only meloxicam helped.

Sixty days is shorter than McCarthy’s seventy, and supplement makers often say glucosamine needs time to work. That’s a fair point, but it doesn’t explain why two prescription drugs showed clear, measurable changes in the same window while the supplement showed none.

Why owners see improvement anyway

If the placebo-controlled trials show so little, why do so many owners swear their dog moves better on glucosamine? A 2012 study from the University of Minnesota offers a big part of the answer.

Conzemius and Evans looked at 58 arthritic dogs that had received only a placebo during a larger drug trial. Force plate readings showed these dogs’ weight bearing stayed flat. Yet owners judged that their dogs improved, when the plate showed no change or a decline, about 40% of the time. Veterinarians did the same 43 to 45% of the time, depending on whether they watched the dog walk, trot, or examined its joints. The effect grew stronger as the study went on.

The researchers called this the caregiver placebo effect. The dog isn’t fooled; the dog doesn’t know it’s in a study, but the people watching the dog are. We want our dogs to feel better, we know we started something, and we notice the good days more.

A 2017 trial from the same group shows the effect in a glucosamine study specifically. Scott and colleagues gave 60 arthritic dogs either a glucosamine and chondroitin product or a placebo for 90 days. Every dog wore an activity monitor around the clock. Activity didn’t differ between the groups. Owner questionnaire scores improved in both groups, by about the same amount, so the owners of placebo dogs saw the same “improvement” as owners of supplement dogs.

What the reviews concluded

Overall, the reviews have moved from “uncertain” to “don’t recommend it for pain” over the past 15 years.

Aragon, Hofmeister, and Budsberg (2007). This systematic review graded 16 osteoarthritis trials in dogs using an FDA evidence-scoring system. Meloxicam came out with the strongest support. Glucosamine and chondroitin did not earn the same confidence.

Bhathal and colleagues (2017). This narrative review, the one I flagged at the end of Part 1, surveyed the canine research and reached a cautious verdict. The products look safe, but clinical benefit remains questionable. The authors also noted that veterinarians commonly recommend them anyway, often as a way to reduce reliance on NSAIDs.

Barbeau-Grégoire and colleagues (2022). This is the most rigorous look so far: a registered systematic review and meta-analysis of 72 trials from 57 papers, covering nine categories of joint supplements and therapeutic diets in dogs and cats. Omega-3 diets and supplements showed clear pain relief, and CBD showed some. Collagen was weak. For glucosamine and chondroitin, the authors found a strong non-effect and recommended that these products no longer be recommended for osteoarthritis pain.

Kampa and colleagues (2023). The newest placebo-controlled trial tested a widely sold glucosamine, chondroitin, and MSM chew against carprofen, two marine oil products, and a sunflower oil placebo in 75 dogs with hip arthritis. After six weeks, carprofen and both marine oils significantly improved force plate scores over placebo. The glucosamine group did not. Two caveats here: the trial was funded by the maker of the marine oil products, and the authors themselves noted six weeks may be too short for glucosamine.

The honest case still made for glucosamine

The evidence leans against glucosamine for pain, but the people who still use it aren’t being foolish. Here is the best case, stated fairly:

• Time. The trials showing nothing ran six to 13 weeks. McCarthy’s positive result appeared at 10 weeks. Glucosamine is supposed to support cartilage slowly, and few trials have followed dogs for six months or more. Scott’s 90-day trial did not find a benefit, so the time argument is weaker than it sounds, but it isn’t settled.
• Pain isn’t the only question. Most trials measured pain and weight bearing. The original theory was that glucosamine helps preserve cartilage, which would show up as slower disease progression over years, not faster relief in weeks. That has not been well tested in arthritic dogs.
• Safety. Across these studies, glucosamine and chondroitin caused few problems. NSAIDs work much better, but they carry real risks for some senior dogs, especially those with kidney or liver concerns. For a dog that can’t take NSAIDs, a low-risk option can look appealing even with weak evidence.
• Products vary. Every trial tested a different formulation, dose, and combination. A null result for one product does not prove every product fails, though it does shift the burden of proof onto the products.

What the case does not support is the confident language on most labels. “Clinically proven joint support” rests mostly on studies like McCarthy’s, which can’t rule out the placebo effect.

What this means for your senior dog

Put Part 1 and Part 2 together and the picture is consistent. A small share of oral glucosamine reaches the bloodstream, and in the best-designed trials, that hasn’t translated into measurable pain relief.

If you’re deciding what to do for an arthritic dog, here is how I’d use this research:

1. Don’t let a supplement stand in for pain control. If your dog is limping, struggling with stairs, or slowing on walks, that’s pain worth treating. Talk to your vet about options that have strong evidence behind them.
2. If you try glucosamine anyway, decide in advance how you’ll judge it. Pick specific things you can count, like how many steps before the limp eases or how long a walk takes. Write down a baseline before starting. That’s the closest an owner can get to a force plate, and it guards against the caregiver placebo effect.
3. Give it a fair, fixed trial. Ask your vet about a set period, then honestly reassess against your baseline. Stop if nothing measurable changed.
4. Bring the research to your vet. Many vets still suggest glucosamine as a low-risk add-on, and they may have good reasons for your dog specifically. Ask what they’ve seen and what they’d watch for.

The most interesting finding in the 2022 meta-analysis wasn’t about glucosamine. It was that omega-3 enriched diets and supplements showed clear benefit, and so did the two marine oil products (green-lipped mussel and krill based) in the 2023 trial. That’s where Part 3 goes next: chondroitin, MSM, omega-3s, and the rest of the supplement stack, ingredient by ingredient, with the same questions about absorption and evidence.

Sources

Aragon CL, Hofmeister EH, Budsberg SC. Systematic review of clinical trials of treatments for osteoarthritis in dogs. J Am Vet Med Assoc. 2007;230(4):514–521.

Barbeau-Grégoire M, Otis C, Cournoyer A, Moreau M, Lussier B, Troncy E. A 2022 systematic review and meta-analysis of enriched therapeutic diets and nutraceuticals in canine and feline osteoarthritis. Int J Mol Sci. 2022;23(18):10384. [Open access.]

Bhathal A, Spryszak M, Louizos C, Frankel G. Glucosamine and chondroitin use in canines for osteoarthritis: a review. Open Vet J. 2017;7(1):36–49. [Open access.]

Conzemius MG, Evans RB. Caregiver placebo effect for dogs with lameness from osteoarthritis. J Am Vet Med Assoc. 2012;241(10):1314–1319.

Kampa N, Kaenkangploo D, Jitpean S, et al., Lascelles BDX. Study of the effectiveness of glucosamine and chondroitin sulfate, marine based fatty acid compounds (PCSO-524 and EAB-277), and carprofen for the treatment of dogs with hip osteoarthritis. Front Vet Sci. 2023;10:1033188. [Open access.]

McCarthy G, O’Donovan J, Jones B, McAllister H, Seed M, Mooney C. Randomised double-blind, positive-controlled trial to assess the efficacy of glucosamine/chondroitin sulfate for the treatment of dogs with osteoarthritis. Vet J. 2007;174(1):54–61.

Moreau M, Dupuis J, Bonneau NH, Desnoyers M. Clinical evaluation of a nutraceutical, carprofen and meloxicam for the treatment of dogs with osteoarthritis. Vet Rec. 2003;152(11):323–329.

Scott RM, Evans R, Conzemius MG. Efficacy of an oral nutraceutical for the treatment of canine osteoarthritis: a double-blind, randomized, placebo-controlled prospective clinical trial. Vet Comp Orthop Traumatol. 2017;30:318–323.

Adebowale A, et al. 2002, cited for the ~12% figure, is listed in full in Part 1.