Last updated October 19, 2026
Ascophyllum nodosum is a brown seaweed from the North Atlantic, also called knotted wrack or rockweed, that is dried and fed to dogs to slow the build-up of plaque and tartar. In the one placebo-controlled dog trial published in a journal, a daily dose kept tartar 20 to 35% lower than placebo over 90 days, and plaque 38% lower by day 90, on teeth a vet had just cleaned.
It doesn't remove tartar that has already hardened, and it doesn't replace brushing. It is also rich in iodine, so a dog with a thyroid condition, or on thyroid medication, should only have it after a word with your vet. For seaweed in general, see can dogs eat seaweed.
What Ascophyllum nodosum is
It grows on rocky shores between the tides, with long olive-brown fronds and small air bladders that hold it up in the water. It's often sold as kelp, but it isn't one. True kelps such as kombu belong to a different order of brown seaweeds, and Ascophyllum is a wrack.
For dogs it's dried and milled into a powder, or baked into treats and chews. The species name on the label matters, because the dental trials used this seaweed. "Kelp" or "sea vegetables" on a pack doesn't tell you whether the product resembles what was tested.
What the dog trial found
Gawor and colleagues (2018, Frontiers in Veterinary Science) took 60 small dogs, mostly Chihuahuas and miniature Schnauzers averaging about 4 kg, and cleaned every mouth under anesthesia. Half then ate a daily seaweed treat, about 50 mg of seaweed per kilogram of body weight. The other half got the same treat without seaweed, and nobody scoring the dogs knew which was which.
| Check-up | Tartar vs placebo | Plaque vs placebo | Breath sulfur test vs placebo |
|---|---|---|---|
| Day 30 | 35% lower | No clear difference yet | 24% lower, not a clear difference |
| Day 60 | 22% lower | No clear difference yet | 35% lower |
| Day 90 | 20% lower | 38% lower | 46% lower |
The tartar and plaque percentages are our arithmetic from the published averages. The breath figures are the authors' own.
Both groups built up plaque and tartar again after the cleaning, and the seaweed group did it more slowly.
The maker of the product funded the whole study, one examiner scored every dog, and every dog was a small breed eating treats rather than a powder. A crossover trial in adults points the same way. In it, 61 people with moderate to heavy tartar took 500 mg of the seaweed a day for six months and control tablets for another six, and 55 finished. They formed 52% less new tartar on the seaweed, and 52 of the 55 formed less on the seaweed than on the control tablets (van Dijken and colleagues, 2015, Clinical Oral Investigations). The same maker helped pay for that one too.
How it might work
Nobody knows for sure. The working idea is that compounds from the seaweed are absorbed in the gut and may reach the mouth in saliva, where they might change how plaque forms and hardens. The 2018 authors describe it that way and call the mechanism unclear. The seaweed isn't scrubbing the teeth, because a few small treats a day can't do that.
In a follow-up, the same group gave 60 dogs a seaweed powder or a placebo for 30 days and analyzed their saliva (Gawor and colleagues, 2021). Saliva chemistry shifted one way in the seaweed dogs and a different way in the placebo dogs. The study couldn't say which change, if any, is the one that slows plaque. So treat the saliva route as a reasonable hypothesis, not a finding.
Who paid for the research, and what's missing
Every published study on Ascophyllum and teeth that we found traces back to one manufacturer. That doesn't make the results wrong, but nobody independent has repeated them yet.
A 2023 review by Gawor and Jank (Polish Journal of Veterinary Sciences) says the only test on existing dental disease, in cats, found no benefit. The review lists that cat study as unpublished data, so nobody outside the authors can check it.
The Veterinary Oral Health Council (VOHC) has given its seal to several products from that maker, for plaque and for tartar. Each claim needs two trials showing at least 15% less build-up than a control over 28 days or more, on teeth scaled clean at the start. We couldn't find most of those trials in print. The seal also belongs to each named product, not to the seaweed, so it says nothing about another brand's powder.
The dog studies from university teams that we found looked at taste and digestion, not teeth.
Is Ascophyllum nodosum safe for dogs
In the 2018 trial, owners saw no digestive upset and every dog ate its treats, so the safety question that remains is iodine.
Brown seaweeds as a group hold 2,500 to 10,000 micrograms of iodine per gram dried (Smyth, 2021, European Thyroid Journal). The batch in the 2018 trial measured 450 to 1,000. So iodine can differ several-fold between sources, and the species name alone won't tell you how much a product carries. The trial dogs took in about 19 micrograms per kilogram of body weight a day.
The thyroid gland uses iodine to make its hormones, and too much can unbalance it, as can too little. The 2018 trial checked thyroid hormone only at the start, to enroll dogs with normal levels, and didn't re-test it at any later check-up. It tells us nothing about what months of daily seaweed do to a dog's thyroid.
Ask your vet before starting any Ascophyllum product if your dog
- has a thyroid condition or takes thyroid medication
- has kidney disease
- is pregnant or nursing
- is a puppy (check the minimum age on the pack)
- takes other daily medication, or another supplement with seaweed or iodine in it
Never swap a thyroid medicine your vet prescribed for a supplement.
Taste, digestion and the other claims
Some dogs dislike the taste. In a test by a University of Perugia team, 11 dogs were offered plain kibble beside kibble with 1% Ascophyllum, and in the first five minutes they ate only about a third as much of the seaweed food. At 0.3% there was no difference. Which bowl they went to first showed no preference, so the authors put it down to taste rather than smell (Isidori and colleagues, 2019, Journal of Applied Phycology). A dog that starts leaving food once the seaweed goes on may not like it.
The gut study found nothing either way. Ten healthy dogs fed Ascophyllum, and three other seaweeds, at 15 g per kilogram of food for four weeks each showed no change in their stools, gut bacteria or digestion (Pinna and colleagues, 2021, Animals). We couldn't find a controlled dog trial for coat, joints or immunity, so we don't claim any of them.
What it won't do
The trial started on clean teeth, and Ascophyllum slows new build-up. It doesn't dissolve brown, hardened tartar, and the 2023 review recommends it after a professional cleaning, to slow the return. If your dog's teeth already carry tartar, start with your vet. Our guide to what happens at a dog dental cleaning walks through the day.
Brushing with a soft brush and dog toothpaste is still the method with the strongest trials behind it. We rank every home method by its evidence in how to clean your dog's teeth at home. A seaweed product fits beside the brush, or as the fallback for a dog that won't allow one.
Red or bleeding gums, a loose or broken tooth, swelling on the face, or a dog that has gone off its food all need a vet, not a supplement.
Choosing a seaweed product
The species written out in full on the label is the first check. Labels often leave out the rest.
- The amount by body weight. The trial gave about 50 mg of seaweed per kilogram a day.
- Iodine per daily amount, from a batch test. If it isn't printed, ask the maker.
- A VOHC seal, if the maker claims one, on that exact product on the VOHC list.
Caniclean is our seaweed powder. It goes on your dog's food every day, with the amount for each body weight printed on the pack, and it helps reduce plaque and new tartar. It isn't VOHC-accepted. On taste, Emma Starkey wrote in a verified review on January 16, 2024, "my dog has no hesitation in eating it! I just sprinkle it over her normal food."
Questions owners ask
Is Ascophyllum nodosum the same as kelp?
No. It's a wrack, a different group of brown seaweed from true kelps such as kombu, though labels often call it kelp. Both carry a lot of iodine. Of the two, only Ascophyllum has been tested on dog teeth in a controlled trial.
How long does Ascophyllum nodosum take to work?
In the 2018 trial, tartar was already lower than in the placebo group at 30 days. The breath test took until day 60 to show a clear difference, and plaque until day 90. Give it about three months of daily use, ideally starting on freshly cleaned teeth, before you judge it.
Can puppies have Ascophyllum nodosum?
Follow the minimum age on the pack and ask your vet first. The youngest dog in the trial was 10 months old, so there's no trial data on young puppies.
Can I give my dog a human Ascophyllum supplement?
It's better not to. Human capsules aren't dosed by a dog's weight and may not list their iodine, which matters most for a small dog. Some also contain other ingredients.
References
- Gawor J, Jank M, Jodkowska K, Klim E, Svensson UK. Effects of edible treats containing Ascophyllum nodosum on the oral health of dogs, a double-blind, randomized, placebo-controlled single-center study. Front Vet Sci. 2018;5, 168. doi:10.3389/fvets.2018.00168
- Gawor JP, Wilczak J, Svensson UK, Jank M. Influence of dietary supplementation with a powder containing Ascophyllum nodosum algae on dog saliva metabolome. Front Vet Sci. 2021;8, 681951. doi:10.3389/fvets.2021.681951
- Gawor J, Jank M. Ascophyllum nodosum as a nutrient supporting oral health in dogs and cats, a review. Pol J Vet Sci. 2023;26(3), 511-520. doi:10.24425/pjvs.2023.145053
- van Dijken JWV, Koistinen S, Ramberg P. A randomized controlled clinical study of the effect of daily intake of Ascophyllum nodosum alga on calculus, plaque, and gingivitis. Clin Oral Investig. 2015;19(6), 1507-1518. doi:10.1007/s00784-014-1383-2
- Isidori M, Rueca F, Trabalza-Marinucci M. Palatability of extruded dog diets supplemented with Ascophyllum nodosum L. (Fucaceae, Phaeophyceae). J Appl Phycol. 2019;31, 3275-3281. doi:10.1007/s10811-019-01799-5
- Pinna C, Vecchiato CG, Grandi M, Stefanelli C, Zannoni A, Biagi G. Seaweed supplementation failed to affect fecal microbiota and metabolome as well as fecal IgA and apparent nutrient digestibility in adult dogs. Animals. 2021;11(8), 2234. doi:10.3390/ani11082234
- Smyth PPA. Iodine, seaweed, and the thyroid. Eur Thyroid J. 2021;10(2), 101-108. doi:10.1159/000512971
- Veterinary Oral Health Council. Accepted products and trial protocol requirements. https://vohc.org/accepted-products/ and https://vohc.org/trial-protocol-requirements/