Most joint products for cats are sold on a mechanism, not on an outcome. The ingredients with a defensible daily dose are few: omega-3 fatty acids at 25 to 40 mg/kg of combined EPA and DHA, green-lipped mussel at 50 to 100 mg/kg, and glucosamine at 20 to 30 mg/kg on much thinner proof. Everything else on the shelf is optional spending. The habit that makes any of it judgeable is a written mobility score and a review at 12 weeks, not a 14 day impression.
Three tiers of evidence, in plain terms
Tier A means repeatable benefit in controlled trials plus years of use in cats. Tier B means small feline trials or consistent clinical reports, with no large trial either way. Tier C means a plausible pathway and nothing more. Most feline practitioners work in tiers B and C for joints, which is acceptable as long as the owner knows that the 12 week score, not the label, is the test. Expect $18 to $45 per month for a 4.5 kg cat, and plan to drop 2 of the 3 products below if the score has not moved by week 12.
Omega-3: the one with a real dose
EPA and DHA are the only joint ingredients with a dose most veterinarians will state out loud: 25 to 40 mg/kg per day of the 2 combined, which is 110 to 180 mg for a 4.5 kg cat. Start at 25 mg/kg for 7 days, then step to 35 mg/kg. Loose stool in the first week is common and usually settles by day 10; if it does not, halve the dose for 5 days and climb again. The ceiling matters more than the floor: past 60 mg/kg per day the extra calories (9 kcal per gram of oil) and the GI risk rise without added benefit. Stop 7 days before any surgery, and ask first if the cat is on an anticoagulant. Full effect takes 6 to 8 weeks.
Label math: 4 numbers before you buy
Most failures are arithmetic, not biology. A 500 mg fish oil capsule that is 30 percent EPA plus DHA delivers 150 mg, so a 4.5 kg cat at 35 mg/kg needs 158 mg, which is 1 capsule, not 3. A concentrated 1,000 mg capsule at 60 percent delivers 600 mg, so 1/4 capsule covers the same cat, or about 0.25 mL of liquid oil. Read 3 more lines on the label: vitamin A and D (cod liver oil carries both, and 5 mL daily can overshoot a safe vitamin A intake within 8 weeks), the peroxide value or expiry date (rancid oil is refused by most cats), and whether the milligrams are total oil or total EPA plus DHA.
Glucosamine and chondroitin: tier C for cats
Glucosamine at 20 to 30 mg/kg with chondroitin at 10 to 15 mg/kg, so roughly 90 to 135 mg plus 45 to 68 mg daily for a 4.5 kg cat, is the best selling combination and the weakest supported. Large human knee trials and later pooled analyses mostly found no difference from placebo for pain, and no feline trial is large enough to argue the other way. It is low risk: the safety record in cats is good, mild GI upset is uncommon, and it does not clash with standard pain drugs. Treat it as a 12 week trial at 250 mg glucosamine per day, judged on the score, with an honest expectation of no change.
Green-lipped mussel: tier B and the easiest sell
Green-lipped mussel powder at 50 to 100 mg/kg per day, which is 225 to 450 mg for a 4.5 kg cat, has the most feline-specific reporting behind it: small placebo-controlled trials described better activity and less stiffness after 4 to 6 weeks, and clinicians reach for it when an owner wants 1 product instead of 3. It also carries omega-3, so do not stack it on a full fish oil dose — pick one, or halve both. Mussel is a shellfish protein, so skip it if the cat has reacted to seafood.
3 ingredients to skip, and 1 rule
MSM at 25 to 50 mg/kg, cetyl myristoleate, and collagen peptides appear in most blends; none has feline outcome data, and a single blend can carry all 3 at doses too low to matter. Skip anything dosed for dogs at 2 tablets per 10 kg, and do not add high dose turmeric to an NSAID without asking, because that pair raises GI risk. The rule: if a label lists 12 ingredients and 0 milligrams, it is a marketing object, not a dose.
The evidence table
| Ingredient | Daily dose for 4.5 kg | Tier | First thing to check | Cost per month |
|---|---|---|---|---|
| Omega-3 (EPA + DHA) | 110 to 180 mg | B | Stool quality at day 10 | $18 to $30 |
| Green-lipped mussel | 225 to 450 mg | B | Shellfish reaction, week 1 | $22 to $40 |
| Glucosamine + chondroitin | 90 to 135 mg + 45 to 68 mg | C | Vomiting or loose stool at week 2 | $12 to $25 |
| MSM | 110 to 225 mg | C | Nothing established | $10 to $20 |
| Collagen peptides | 100 to 250 mg | C | Protein load in kidney disease | $9 to $18 |
Safety and the 6 month bloodwork
These products are not inert. High dose fish oil adds calories and can loosen stool; mussel adds protein and iodine; marine oils can affect platelet function at 60 mg/kg and above. A cat over 10 that starts any of them should have a chemistry panel and a T4 at baseline, then again at 6 months, because that second visit is when early kidney or thyroid disease usually surfaces. Refrigerate liquid oil and finish an opened bottle within 60 days.
The 12 week evaluation node
Score 5 movements on day 0 and then every 4 weeks: jump height in centimeters, seconds to lie down, stairs climbed per day, minutes of self grooming, and distance walked without stopping. At week 12, the 3 month mark, there are 3 outcomes. A gain of 2 points or more on a 20 point scale means continue for another 6 months and re-score at week 24. No change means stop everything except omega-3, if the coat and kidney markers justify it. A loss of 2 points or more means stop the supplements and book an examination with radiographs, because a supplement that fails is a diagnostic prompt, not a reason to double the dose. The same week, weigh the cat and compare it with the number recorded 12 weeks earlier on the weight trend sheet; a 3 percent loss with a flat mobility score points to something other than arthritis.
What to do this week
- Weigh the cat and write the number on the score sheet, so week 12 has a baseline.
- Pick 1 product, compute milligrams per kilogram, and note it on the sheet.
- Start at 25 mg/kg of EPA plus DHA, step up after 7 days.
- Photograph the label and the expiry date; most bottles are opened and forgotten.
- Book the 12 week review now, and price the year at the cost calculator before committing.
A cat that hesitates at doorways in dim light may have a seeing problem rather than a joint one; see vision loss in senior cats.
Terms mentioned in this article
Frequently asked
Can I give my cat human fish oil capsules?
Yes, if you do the milligram math and check the label for added vitamin A and D. A 4.5 kg cat needs 110 to 180 mg of combined EPA and DHA per day, which is often 1 capsule of a 500 mg product or a quarter of a concentrated one. Prick the capsule and mix the oil into wet food, keep the bottle in the fridge, and stop 7 days before surgery.
How long before I know a joint supplement is working?
Give it 6 to 8 weeks to reach full effect and judge at 12 weeks with a written score of 5 movements, because owner impressions drift within 2 weeks. If the 20 point total has not moved by week 12, stop the product rather than raising the dose, and book an examination with radiographs.
Is glucosamine worth buying if trials were negative?
It is low risk and low expected benefit. Large human trials found little difference from placebo for pain, and no feline trial is large enough to settle it, so a 12 week trial at 250 mg per day is reasonable if you score the result instead of guessing. Keep it only if the score improves by 2 points or more.