Quick answer: an underactive thyroid (hypothyroidism) can make a dog slow, heavy and reluctant to exercise, which looks a lot like stiff joints, so get the thyroid diagnosed and treated first and see how much of the stiffness lifts. If your dog still struggles once their levels are right, a joint supplement can be discussed with your vet. The practical points are timing (thyroid tablets need a consistent routine around food), weight, and avoiding kelp or seaweed products, which can upset thyroid treatment. If your vet agrees, show them the label of MedPaw Hip & Joint Chews and ask whether it suits your dog.
Transparency note: this page is written by MedPaw, which makes a joint supplement. It is general information, not a diagnosis or treatment plan, and it doesn't replace your vet's advice. Sources are linked so you can check them. Checked 9 October 2026.
Is it the thyroid or the joints?
According to CVS Vets, dogs with hypothyroidism "often experience lethargy, excessive weight gain and exercise intolerance", and the condition can also affect the nervous system. All of those can be mistaken for arthritis, and a dog with both problems will feel worse than one with either. The good news is that hypothyroidism has an excellent outlook with treatment. CVS says lethargy and dullness may start improving within a few days of starting medication, and many dogs lose up to 10% of their bodyweight in the first three months.
What to check in a joint supplement for a dog with hypothyroidism
| What to check | Why it matters | What to ask your vet |
|---|---|---|
| Timing | Food reduces absorption of thyroid medicine, so the daily routine needs to stay the same | When should the chew go in relation to the tablet? |
| Kelp, seaweed and iodine | Kelp's iodine content is unpredictable and can interfere with thyroid treatment | Is there anything on this label that affects the thyroid? |
| Calories | Hypothyroid dogs may need a calorie-restricted diet | Should I count the chew as part of the daily food? |
| Blood tests | Thyroid treatment is monitored with blood tests | Should I mention supplements before each test? |
| Other conditions | Older dogs often have more than one condition or medicine | Does the chew suit everything else my dog has? |
For guidance only. Your vet manages your dog's thyroid treatment.
Fitting a joint chew around thyroid tablets
Hypothyroidism is managed with a thyroid hormone tablet or liquid (levothyroxine), usually for life. CVS notes that "absorption is reduced by food" and that it is important to keep the timings of medication and feeding consistent each day. We're not aware of evidence that the common joint actives interact with levothyroxine, but a chew is still food. The simplest approach is to agree a fixed routine with your vet, for example the tablet and the chew at the same times each day, and stick to it, so blood test results reflect a steady pattern.
Avoid kelp and seaweed supplements unless your vet says otherwise
Some "natural" supplements for dogs contain kelp or seaweed, often marketed for the thyroid. A veterinary review of kelp explains that kelp's iodine content is unpredictable, that it can push some animals towards either an underactive or overactive thyroid, and that taking kelp alongside levothyroxine could tip a dog into having too much thyroid hormone. The dog-specific evidence is limited, but it's an easy risk to avoid. Check every supplement label for kelp, seaweed or "marine algae", and see our guide to seaweed for dogs. Kelp and iodine aren't among MedPaw's listed actives.
When to see your vet
- Your dog is still slow, stiff or heavy after the thyroid treatment has had time to work
- Restlessness, panting, weight loss, a fast heartbeat or drinking more after a dose change
- Limping, crying out, or reluctance to use stairs or jump
- Weakness, wobbliness or a head tilt
- Any change after starting a new supplement or food
What helps stiff joints in a hypothyroid dog
Weight is the big one. AAHA's senior care guidelines note that dogs with hypothyroidism "may require a diet that has restricted calories", and every kilo lost takes load off sore joints. Our guide to why dogs gain weight covers thyroid and other causes, and weight loss for stiff dogs has a practical plan. As energy returns, build exercise up gradually with short, steady walks (see low-impact exercise), and ask about hydrotherapy if your dog needs gentle muscle-building. If your dog has lost muscle, our muscle loss guide explains what helps.
What the evidence says about joint actives
A 2022 review of 72 trials graded the common joint supplement ingredients for dogs with arthritis:
How the main joint supplement ingredients compare on evidence for joint pain in dogs
| Ingredient | What the 2022 review of 72 trials found |
|---|---|
| Omega-3 (fish oil, green-lipped mussel) | The strongest evidence of the supplements reviewed |
| Glucosamine and chondroitin | Did not relieve pain |
| MSM, hyaluronic acid, Boswellia | Too few good trials to judge on their own |
Source: Barbeau-Grégoire et al., International Journal of Molecular Sciences, 2022.
Fish oil is the most studied omega-3 source, but it adds calories, which matters for a dog on a calorie-controlled diet. Ask your vet how it fits. See omega-3 fish oil for dogs' joints.
MedPaw's label, to show your vet
MedPaw doesn't treat hypothyroidism or arthritis, and we don't claim it suits every dog with a thyroid condition. Here are its published actives and allergens:
MedPaw Hip & Joint Chews: the main amounts per chew on the label, to show your vet
| Ingredient or fact | Per chew, as published |
|---|---|
| MSM | 185mg |
| Glucosamine | 170mg |
| Chondroitin | 70mg |
| Green-lipped mussel | 70mg |
| Boswellia serrata | 30mg |
| Hyaluronic acid | Included (amount not published) |
| Vitamin C | 33mg |
| Vitamin E | 24 IU |
| Zinc | 3mg |
| Format | Soft chicken and bacon flavour chew, 60 per tub |
| Allergens | Mollusc (green-lipped mussel) and gluten (brewer's yeast) |
| What it is | A complementary feed, not a medicine or painkiller |
The full composition and analytical constituents are printed on the tub.
Our recommendation: treat the thyroid first and give it time. If your dog is still stiff once their levels are stable, and your vet agrees, MedPaw puts glucosamine, chondroitin, MSM, green-lipped mussel, hyaluronic acid and Boswellia into one soft chew that's easy to give at the same time every day, with a 60-day money-back guarantee. Take the label to your vet and ask whether MedPaw Hip & Joint Chews suits your dog. Feeding amounts by weight are on the product page.
Joint supplements and hypothyroidism: common questions
Can hypothyroidism cause stiffness or limping in dogs?
It can make dogs lethargic, heavy and unwilling to exercise, and can affect the nervous system, all of which can look like joint problems. Ask your vet to check, and see how your dog moves once thyroid treatment has had time to work.
Can I give a joint supplement with levothyroxine?
Many dogs have both, with their vet's agreement. Because food reduces absorption of thyroid medicine, agree a fixed daily routine for the tablet and any chew, and keep it the same every day.
Should I avoid kelp if my dog has an underactive thyroid?
Yes, unless your vet recommends it. Kelp's iodine content is unpredictable and may interfere with thyroid treatment. Check supplement labels for kelp, seaweed or marine algae.
Will my dog's stiffness improve once the thyroid is treated?
Often energy, weight and willingness to exercise improve, which can make a big difference to how a dog moves. If stiffness remains, it may be arthritis, and your vet can examine your dog.
Do joint supplements affect thyroid blood tests?
We're not aware of evidence that common joint actives change thyroid results, but tell your vet about every supplement before blood tests so they can interpret them with the full picture.
