If you've ever shopped for a horse ulcer supplement, you know the feeling. Dozens of products, every one claiming to be the best. But most of them don't really differ by brand. They differ by a handful of active ingredients that show up again and again on every label. So we're flipping the comparison around. We explain the ingredients, what they actually do, and how good the evidence is. Which products contain which ingredients comes after, in one table you can scan.
One thing up front: A supplement is not a drug. If your horse has a diagnosed ulcer or serious symptoms, the first call is always your veterinarian.
For most gastric supplements, there's little solid research in horses. Where data exists, it's often mixed. That doesn't mean nothing helps. It means you should take marketing claims with a grain of salt.
So we go ingredient by ingredient, grouped by what each one is trying to do in the stomach: buffer acid, protect the lining, or work indirectly through the diet. For each, you'll find what it does, how well that's backed up, and what to watch for. Then the table shows which products use which ingredients, so you can apply what you've read yourself. For a deeper dive into how acid buffers, mucosal protectants and acid blockers each work, see our companion guide, Gastric protectants, acid buffers or acid blockers.
Two products aren't supplements at all. They're FDA-approved drugs, and they belong at the top because they're the benchmark everything else is measured against. Both are omeprazole, a proton pump inhibitor that turns acid production down at the source.
GastroGard (omeprazole, 4 mg/kg) is prescription-only and FDA-approved to treat equine gastric ulcers. It has by far the best evidence and is the gold standard for a diagnosed ulcer.
UlcerGard is the same omeprazole at 1 mg/kg, available over the counter, and FDA-approved to prevent ulcers during stressful times like travel, showing or stall rest. It's the only FDA-approved product specifically labeled for prevention.
Everything that follows is an over-the-counter supplement. These don't replace omeprazole for active disease. They support it, help with the daily acid load, or carry a horse through the period right after treatment. One useful point for the buffers below: while omeprazole is working, there's little excess acid in the stomach, so there's less for an added buffer to do.
Buffers neutralize excess stomach acid and raise the pH. They don't block anything. They soak up what's already there. That's a smart move for prevention and for the weeks after a treatment course. But the details matter.
Bicarbonate and calcium carbonate are the simplest buffers. Bicarbonate is the same thing a horse's own saliva uses to neutralize acid, and every chew makes more of it. As an additive it works fast, but only briefly, so it's the yardstick the longer-acting buffers get measured against.
Calcified red algae (Lithothamnion) is the most important buffer ingredient, and the most misunderstood. As it grows, the algae stores calcium and magnesium carbonate in its cell walls, forming a porous, sponge-like structure that binds excess acid. It shows up on labels under a lot of names: Lithothamnion, marine-derived calcium, calcareous marine algae, Aquamin, Maerl. And here's the catch: those words tell you almost nothing about how well it actually buffers. Two things decide that, and neither is on the front of the bag.
The first is the species and where it grows. "Red algae" covers several different species grown in very different waters, and the growing conditions shape the microscopic structure. Algae that grows slowly in cold, clean water builds a denser, more porous skeleton with far more surface area, and surface area is what soaks up the acid. The gap is real: by the raw-material supplier's own measurements, cold-water Icelandic algae has roughly five to six times the surface area of the same genus grown in warm Brazilian waters. Same first name on the label, very different performance. The second is purity. Marine algae can take up heavy metals, so independent lab testing and food-grade quality matter more than any term on the bag.
This is where products that look alike on the label part ways. Plenty of them list a marine- or seaweed-derived calcium that reads much the same on the bag, even though the species it comes from, where it was harvested and how clean it is can change the result, and none of that fits on the front label. Equine 74 Gastric, for example, is built exclusively on one species, Lithothamnion glaciale, harvested slowly in the cold, clean waters off Iceland and tested to food-grade quality. A peer-reviewed in-vitro study found it buffered stomach acid for 4 to 6 hours.
Magnesium oxide is a buffer in its own right, a basic oxide that reacts with stomach acid. It's a well-established antacid that often pairs with red algae. One label-reading tip: only the basic magnesium forms (oxide, hydroxide, carbonate) buffer acid. Organic forms like magnesium citrate or glycinate are built to be absorbed into the bloodstream. They deliver magnesium as a nutrient, say, for a calming effect, but they barely touch acid.
Aluminum-based antacids (aluminum phosphate, dihydroxyaluminum sodium carbonate) show up in several US buffer products like RiteTrac and Neigh-Lox Advanced. They're effective acid neutralizers. If you'd rather feed a marine-mineral buffer, that's a label distinction worth knowing, not a knock on either one.
A common promise in this group is "neutralizes stomach acid," as if that were a permanent fix. In reality a good buffer keeps the stomach balanced for hours but doesn't shut acid off. That's why you feed it regularly, ideally split across the day.
These ingredients aim to form a protective film or feed the lining. This is also where the best evidence among supplements sits, thin as it is.
Pectin and lecithin are often used together and have the most data behind them, though it's mixed. Pectin swells in the stomach and can form a gel-like layer over irritated tissue, and lecithin is said to strengthen it. Studies showed improved ulcer scores but no measurable change in stomach pH. Plausible and worth a try, but not a proven substitute for treatment. Egusin and parts of SmartGut Ultra build on this combination.
Sea buckthorn gets marketed as a special protectant for the stomach lining and shows up in products like SmartGut Ultra. The evidence is genuinely mixed. In studies it showed little benefit for the upper (squamous) region and some possible benefit lower down, and it's usually tested inside combination formulas, so it's hard to credit sea buckthorn on its own.
Glutamine, slippery elm, marshmallow root and licorice (DGL) are the soothing crowd: an amino acid building block plus traditional mucilage herbs. Physiologically reasonable, gentle, and largely unproven in controlled studies. GastroElm Plus is basically a blend of soothing herbs. Visceral+ pairs glutamine and mucilage herbs with yeast for the hindgut.
Hyaluronic acid and beta-glucan are a newer mucosal class, and Relyne GI is the main example. The idea is to support the mucosal barrier rather than buffer acid, and it doesn't change stomach pH.
One whole group works indirectly. Instead of buffering or coating the stomach, these options improve the overall diet and the gut as a whole. The most basic version is structure: more fiber means more chewing, more chewing means more saliva, and saliva buffers acid naturally with its own bicarbonate. A "gastric" feed mostly works by swapping high-starch grain for more fiber, so the horse chews more and buffers more acid on its own. That's good management, not a magic ingredient.
A second indirect route reaches further back, into the hindgut. Supplements like SUCCEED support the large intestine and the microbes that ferment fiber there. That matters for the stomach because the two aren't separate problems: both are driven by the same setup of too much grain and too little forage, and an unsettled hindgut adds stress and discomfort that work against a healing stomach. Keep the hindgut working well and you usually help the stomach too. It's a whole-horse approach, not a targeted stomach fix.
And that points to the real foundation no supplement can replace: good forage, and keeping it in front of your horse as much of the day as you can. A horse's stomach makes acid around the clock, and the horse is built to graze almost constantly. Long stretches without hay are one of the biggest risk factors there is. Good-quality hay is the best foundation whenever you can get it. You'll often hear the US advice to feed a little alfalfa before work, since its calcium and protein help blunt the acid splash during exercise. It can do that, but alfalfa's coarse, stemmy structure isn't ideal for a sensitive stomach, so reach for good hay instead whenever you have it. Even the best supplement can't make up for poor or limited forage.
One last difference isn't about the ingredient but the timing. Most products are made for daily feeding, top-dressed on feed as a powder or pellet, for prevention and the long haul. Alongside those are pastes you give shortly before a known stressor like a trailer ride, a show or a vet visit. They're for those one-off stressful moments, not everyday use.
A paste can take one of two routes: The gastric route uses a buffer, for example red algae plus magnesium oxide, to catch the acid spike, on the idea that a calmer, more comfortable stomach means a calmer horse. That's the type in this comparison, and Equine 74 Stomach Calm Relax is a clean-sport example, given 10 to 30 minutes before the event. The other route is a calming paste that works on the nervous system, and there are plenty of those marketed for the in-gate. They're a separate category, not gastric supplements, and they come with a clean-sport catch: many lean on tryptophan, which sits in a grey zone under USEF rules even when it isn't formally banned, and some contain valerian, which USEF and FEI prohibit outright. So if your horse's tension is pure nerves rather than gut, that's a different aisle, and one to read carefully before a rated show.
Here's how those ingredients map onto actual products. The table lists common US gastric supplements with their key ingredients, so you can put what you read above to work. We also boil cost down to the number that actually matters for comparison: price per day, not the sticker price. A cheap-looking product you feed in big scoops can cost more per day than a premium one fed sparingly.
| Product | Type | Key ingredients | Form | Clean-sport note | From ~$/day* |
|---|---|---|---|---|---|
| Equine 74® Gastric | Acid buffer | Calcified red algae (Lithothamnion glaciale, Icelandic), magnesium oxide, flax | Pellet | Doping-free (FN/FEI/Jockey Club); lab-tested | from ~$2.50 |
| Purina Outlast | Acid buffer | Seaweed-derived calcium, magnesium oxide, cane molasses | Pellet | conforms to competition/racing rules (fed as directed) | from ~$0.66 |
| RiteTrac (KER) | Acid buffer (+ hindgut) | Sodium bicarbonate, calcium carbonate, aluminum antacids, lecithin, EquiShure | Powder | no claim; bicarbonate (TCO2-regulated) | from ~$5.70 |
| Neigh-Lox Advanced (KPP) | Buffer + hindgut | Aluminum antacids, calcium carbonate, yeast/S. boulardii | Pellet | NASC brand; no clean-sport claim | from ~$4.35 |
| U-Gard (Corta-Flx) | Acid buffer | Calcium carbonate, magnesium hydroxide, kaolin, apple pectin, aloe | Pellet | no clean-sport claim | from ~$1.00 |
| Egusin SLH | Buffer + mucosal | Oat fiber/beta-glucan, lecithin, pectin, bicarbonate, Lithothamnion | Powder | label: no prohibited substances | ~$7.60 (21-day course) |
| Zesterra (Pro Earth) | Acid buffer (liquid) | Plant oils, guar gum, orange peel bitters, onion extract, colloidal silver | Liquid | no clean-sport claim | from ~$1.20 |
| SmartGut Ultra (SmartPak) | Mucosal protectant | Sea buckthorn, glutamine, aloe, pectin/lecithin, Ca/Mg carbonate, DGL | Pellet | NASC seal | from ~$2.70 |
| Visceral+ (Mad Barn) | Mucosal + hindgut | Glutamine, threonine, magnesium oxide, meadowsweet, lecithin, yeast | Pellet | "competition safe"; contains meadowsweet (salicylate), check list | from ~$2.55 |
| GastroElm Plus | Mucosal (herbal) | Slippery elm, marshmallow, milk thistle, dandelion | Powder | no claim; herbs not listed-prohibited | from ~$0.55 |
| Equine Elixirs Ulceraser | Mucosal (forage/seed) | Chia, flax, pumpkin & sunflower seed, cabbage (whole-food) | Powder | USEF/FEI screened (LGC lab) | from ~$2.55 |
| Relyne GI | Mucosal protectant | Hyaluronic acid + beta-glucan | Liquid | clean-sport certified | from ~$1.80 |
| GutX (100X Equine) | Mucosal protectant | Hyaluronic acid, beta-glucan, glycerine, CMC | Liquid | USEF/FEI compliant | from ~$0.66 |
| SUCCEED DCP | Hindgut/structural | Oat oil, oat flour beta-glucan, yeast, threonine, glutamine | Granules | no controlled ingredients | from ~$3.40 |
| Equine 74® Stomach Calm Relax | Acute buffer paste (stress) | Calcified red algae, magnesium oxide, Scottish seaweed (gel barrier) | Paste | Doping-free (FN/FEI/Jockey Club); lab-tested | ~$11 per dose |
Clean-sport disclaimer: The clean-sport and doping notes in this table reflect manufacturer statements and publicly listed ingredients as of June 2026, not independent testing by Equine 74. Rules and product formulas change, so always check the current product label against the current USEF/FEI prohibited-substance list before you compete. We accept no liability for competition results.
*"From" price per feeding day at a maintenance dose for a 600 kg (1,320 lb) horse, using the largest pack at regular price (and a subscription discount where one is offered). Day-to-day cost runs higher with smaller packs, and prices vary by seller and promotions, so check current pricing. Egusin SLH is a fixed ~21-day course, not an ongoing daily cost. The paste is a single application, so it's priced per use.
Plenty of other products fit the same three mechanisms, including AniMed Ulc-R-Aid, Finish Line U-7, Platinum Performance Gastric Support, Redmond Daily Gold and the Outlast variants. Read the ingredient list. Once you know which actives a product contains, you can place it using the sections above.
For show horses, the label deserves a second read. In the US, gastric supplements are sold as feed and supplements, not drugs, so the FDA doesn't pre-approve them for efficacy. A NASC Quality Seal (from the National Animal Supplement Council) signals manufacturing quality and adverse-event reporting. It does not prove a product works. Among the products here, SmartGut Ultra carries the NASC seal and Relyne GI advertises third-party clean-sport testing.
The bigger watch-out is ingredients that are banned in competition. USEF and FEI both keep prohibited-substance lists, and several calming and herbal additives show up on them. Devil's claw and valerian are among them, along with herbs like chamomile depending on the governing body. Tryptophan sits in a grey zone: USEF treats it as a nutrient, not a banned substance, even though it's marketed as a calmative. Natural salicylates, from meadowsweet or willow, are controlled too. The practical risk is that a supplement contains one of these without it being obvious. So check the label against the current USEF/FEI list, and lean toward products that state clean-sport testing.
The US market for gastric supplements is big and noisy. It gets a lot more manageable once you think in ingredients instead of brand names. A good buffer soaks up acid. Quality red algae does it for longer than plain bicarbonate. Pectin and mucilage herbs coat the lining gently. A high-forage diet works through saliva. And some marketed ingredients just don't deliver what the label suggests. Read panels that way and the whole shelf makes more sense.
For lasting or serious symptoms, the rule never changes. Vet first. A sure diagnosis of an ulcer only comes from a gastroscopy.