S-methylmethionine (SMM), also known as Vitamin U, is a naturally occurring compound found in cabbage and other crucifers that has been studied for its role in supporting the gastric mucosal lining. DGL (deglycyrrhizinated licorice) is a modified form of licorice root, developed to retain licorice's stomach-supportive properties while removing the compound responsible for its cardiovascular risks. Both are commonly discussed as options for gastritis support, and both have real clinical research behind them, gathered through different mechanisms. This comparison lays out what that research actually shows for each.
What is DGL?
DGL stands for deglycyrrhizinated licorice: licorice root (Glycyrrhiza glabra) with the glycyrrhizin compound removed. Glycyrrhizin is what makes regular licorice risky in large amounts (it can raise blood pressure and lower potassium), so DGL was developed specifically to keep the stomach-supportive parts of licorice while stripping out the part that causes problems.
Licorice has a long folk-medicine history for stomach complaints, but the modern DGL research is more specific. Animal studies show DGL increases prostaglandin synthesis, boosts blood supply to damaged mucosa, and increases both the number of mucus-producing cells and the amount of mucus they produce. (1) That's a mucosal-support mechanism, similar in spirit to what SMM does, but through a different biochemical pathway.
The clinical picture on DGL is mixed, and worth stating honestly. An early double-blind trial of 96 gastric ulcer patients found no significant difference in healing rates between DGL and placebo after four weeks. (2) A separate study found DGL reduced aspirin-induced gastric blood loss when taken alongside aspirin. (3) More recently, a randomized, double-blind, placebo-controlled trial of a licorice extract branded GutGard tested 150 mg daily for 60 days in H. pylori-positive patients: 56% of the GutGard group tested negative on a stool antigen test by day 60, compared with 4% of the placebo group. (4) That's a meaningfully positive result, but it is one product's specific extract, not licorice broadly, and it measured H. pylori suppression rather than mucosal healing directly.
What is S-methylmethionine?
S-methylmethionine (SMM), also called Vitamin U, is the compound naturally found in cabbage, kale, and other crucifers that Garnett Cheney studied at Stanford in the 1940s and 50s for peptic ulcer healing. It's licensed as a pharmaceutical drug in Ukraine (Doctovit) and sold as an OTC stomach medicine in Japan (Cabagin) at doses from 150 mg to 300 mg per day. (5)(6)
The mechanism is different from DGL's. SMM acts as a methyl donor and has been shown in gastric tissue studies to stimulate mucin secretion, the protective mucus layer that coats the stomach wall. (7) A 2023 clinical trial in chronic gastritis patients using 300 mg/day found statistically significant symptom improvement by month three, continuing through month six. (8) Because mucin production and mucosal lining support are relevant regardless of what's driving the gastritis, this mechanism is not specific to any one cause, including H. pylori-related cases. The full research record, including the Cheney trials and the Ukrainian and Japanese pharmaceutical history, is in the Global Vitamin U Research Database.
How do their mechanisms differ?
DGL works primarily by increasing prostaglandin production and mucus-cell activity, and (in the GutGard formulation specifically) has demonstrated activity against H. pylori. SMM works primarily as a methyl donor that stimulates mucin secretion directly and has been studied for structural mucosal support over months of use. Both aim at strengthening the stomach's protective lining, but through separate biochemical routes. This is why some people report a difference trying one over the other: different mechanisms mean different individual responses.
Where the research is stronger for each
DGL's strongest data point is the GutGard H. pylori trial: a specific, targeted piece of antibacterial evidence (H. pylori status can be confirmed with a breath or stool test). DGL's ulcer-healing data, by contrast, is older and weaker: the original gastric ulcer trial found no advantage over placebo. (2)
SMM's strongest data points are the Cheney ulcer-healing trials (7.3 days to heal vs. 42 days on standard treatment) and the more recent Drozdov chronic gastritis trial showing sustained symptom improvement over six months. (5)(8) SMM does not have a dedicated H. pylori antibacterial trial the way GutGard does, but its mucosal-support mechanism (stimulating mucin production and structural repair) is not specific to any single cause of gastritis. That means it is relevant both for chronic, non-bacterial gastritis and as general mucosal support alongside H. pylori treatment, since a person with H. pylori also has an irritated lining that benefits from mucosal repair.
Neither compound has been tested head-to-head against the other in a clinical trial. What follows is a comparison of separate research bases, not a direct competition.
Which one fits which situation?
For confirmed H. pylori infection, standard treatment is antibiotic-based and prescribed by a doctor. DGL's GutGard research is a specific, targeted data point for antibacterial support alongside that treatment. SMM's mucosal-support research applies more broadly: it is relevant for chronic, non-bacterial gastritis and can also support the lining itself during and after H. pylori treatment, since eradicating the bacteria does not by itself repair the mucosa. For a longer maintenance timeline with pharmaceutical history in two countries and structural mucosal support as the primary goal, SMM's research base is the more direct fit.
Cost and form factor also matter in practice. DGL is typically taken as a chewable tablet before meals; SMM is a standard capsule taken with food. Neither is complicated to add to a routine.
Safety and side effects
Both compounds have favorable safety records, with some differences worth knowing.
DGL has a long history of use, and clinical trials have not reported significant adverse effects. Because the glycyrrhizin responsible for whole licorice's cardiovascular risks (elevated blood pressure, lowered potassium) is removed in the deglycyrrhizination process, DGL does not carry those specific risks, which is part of why it is generally considered appropriate for longer-term use. (1)
SMM's safety data shows a similarly clean profile: no serious adverse effects have been documented in published clinical trials at supplemental doses, and a 2025 pharmacological review described its toxicity profile as low across a broad range of organ systems. The most commonly reported mild effect is gastrointestinal discomfort when taken on an empty stomach, which is addressed by taking it with food. The longest published human trial on daily SMM supplementation ran six months; DGL's practical use history is longer, though direct long-term comparative data for either compound beyond that window is limited. See the side effects guide for the full breakdown of what's documented for SMM specifically.
Can you take both?
There's no published research on combining DGL and SMM, and no documented mechanism suggesting a problem doing so; they work through different pathways and don't compete for the same biochemical process. That said, "no evidence of harm" isn't the same as "studied together," so if you're taking DGL and considering adding SMM (or the reverse), it's worth mentioning to your doctor, particularly if you're also on other medications. See the side effects guide for what's known about SMM specifically.
Summary
DGL and SMM are not competing for the same role. DGL's clearest evidence is targeted antibacterial support against H. pylori (in its GutGard form); SMM's clearest evidence is broader mucosal support relevant across gastritis causes, including alongside H. pylori treatment. Neither compound is a cure, and neither has been tested head-to-head against the other. Both are studied, structure/function-level supports for the gastric lining, and the right fit depends on the specific picture: what's driving the gastritis, and what a doctor recommends alongside it.
For how these two stack up against zinc carnosine, mastic gum, and L-glutamine as well, see 5 stomach lining repair supplements that actually work.
This article is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before starting any new supplement, especially if you have a health condition or take medications.
This statement has not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.
References:
1. Deglycyrrhizinated Licorice (DGL) in Promoting Gastric Mucosal Health. Council for Accreditation in Complementary Health Sciences. link
2. Double-blind trial of deglycyrrhizinated liquorice in gastric ulcer. Gut. 1971. https://pubmed.ncbi.nlm.nih.gov/4584640/
3. Effect of deglycyrrhizinated liquorice on gastric mucosal damage by aspirin. 1979. https://pubmed.ncbi.nlm.nih.gov/493863/
4. Puram S, et al. Effect of GutGard in the Management of Helicobacter pylori: A Randomized Double Blind Placebo Controlled Study. Evid Based Complement Alternat Med. 2013. https://pubmed.ncbi.nlm.nih.gov/23606875/
5. Cheney G. Rapid Healing of Peptic Ulcers in Patients Receiving Fresh Cabbage Juice. California Medicine. 1949;70(1):10-15. https://pmc.ncbi.nlm.nih.gov/articles/PMC1643665/
6. Cabagin KOWA Alpha Plus package insert. Kowa Company, Ltd. link
7. Watanabe T, et al. Augmentative Effects of L-Cysteine and Methylmethionine Sulfonium Chloride on Mucin Secretion in Rabbit Gastric Mucous Cells. 2000. https://pubmed.ncbi.nlm.nih.gov/10719747/
8. Drozdov VN, et al. Effect of 6-Month S-Methylmethionine Intake on the Quality of Life and Dyspepsia Symptoms in Patients with Chronic Gastritis. 2023. https://pubmed.ncbi.nlm.nih.gov/37346023/
*This statement has not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.