Zinc carnosine, S-methylmethionine (SMM, also known as Vitamin U), DGL licorice, mastic gum, and L-glutamine are the five compounds that come up most often as stomach lining repair supplements, and each one works through a different mechanism. This post rounds up what the published research actually shows for each, in order of how much comparative trial evidence currently exists.
Zinc carnosine
Zinc carnosine is a chelate compound, a zinc ion bound to the dipeptide L-carnosine, approved as a pharmaceutical (polaprezinc) for gastric ulcers in Japan and Korea. It has one of the more substantial research bases of any compound in this category. The mechanism is prostaglandin-independent cytoprotection and antioxidant activity. (1)
A multicenter, double-blind trial of 258 gastric ulcer patients found 150 mg/day of zinc carnosine produced marked symptom improvement in 75% of patients by eight weeks, comparable to or slightly ahead of a standard comparator drug tested in the same trial. (2) It has also been studied combined with H. pylori triple therapy, where a multicenter randomized trial found it improved outcomes when added to antibiotic treatment. (3)
Zinc carnosine's research base is larger in volume than SMM's and includes more directly comparative trials against pharmaceutical standards. The main long-term safety consideration is that high-dose, long-term zinc intake can interfere with copper absorption. See the full comparison with S-methylmethionine for the complete picture.
S-methylmethionine (Vitamin U)
S-methylmethionine is the compound found in cabbage and other crucifers that has been studied since Garnett Cheney's Stanford ulcer trials in the 1940s. It's licensed as a pharmaceutical in Ukraine and sold as an OTC medicine in Japan. The mechanism centers on stimulating mucin secretion, the protective mucus layer that coats the stomach wall, along with general cytoprotection against irritants like alcohol and NSAIDs. (4)
Cheney's original 1949 trials found cabbage juice, rich in SMM, healed gastric ulcers in an average of 7.3 days compared to 42 days on standard treatment of the era, which is where the "Vitamin U" name comes from. (5) More recently, a 2023 trial in chronic gastritis patients at 300 mg/day found statistically significant symptom improvement sustained through six months. (6) The full research record is compiled in the Global Vitamin U Research Database.
SMM's research base is the only one on this list with documented evidence at both the acute (ulcer healing) and chronic (sustained gastritis symptom improvement) ends, and pharmaceutical use across two countries spanning more than 70 years. It doesn't have a dedicated antibacterial trial against H. pylori; see Vitamin U and H. pylori: what the research actually shows for the full breakdown of that specific question. For the full comparison against two of the other compounds on this list, see S-methylmethionine vs DGL and S-methylmethionine vs zinc carnosine.
DGL licorice
DGL (deglycyrrhizinated licorice) is licorice root with glycyrrhizin, the compound responsible for whole licorice's cardiovascular risks, removed. The mucosal-support mechanism is different from SMM's and zinc carnosine's: animal studies show DGL increases prostaglandin synthesis, boosts blood supply to damaged mucosa, and increases both the number and output of mucus-producing cells. (7)
The human clinical picture is mixed. An early double-blind trial of 96 gastric ulcer patients found no significant difference in healing rates between DGL and placebo after four weeks. (8) More recently, a randomized, double-blind, placebo-controlled trial of a specific licorice extract (branded GutGard) tested 150 mg daily for 60 days in H. pylori-positive patients: 56% of the treatment group tested negative on a stool antigen test by day 60, compared with 4% of placebo. (9) That's a real, targeted result, but it's one product's specific extract measuring H. pylori suppression, not licorice broadly and not mucosal healing directly.
DGL's clearest evidence is antibacterial and specific to the GutGard formulation. Its general ulcer-healing data is older and weaker than that. See the full comparison with S-methylmethionine for the complete mechanism and safety breakdown.
Mastic gum
Mastic gum is a resin from the Pistacia lentiscus tree, grown almost exclusively on the Greek island of Chios. The modern research interest started with a 1998 letter in the New England Journal of Medicine reporting that mastic gum killed H. pylori in laboratory testing, including antibiotic-resistant strains. (10)
Follow-up research has been more mixed. A randomized pilot study testing whether mastic gum could actually eradicate H. pylori in humans did not meet its primary endpoint for statistical significance. (11) Separately, a randomized, double-blind, placebo-controlled trial of 148 patients with functional dyspepsia found that 350 mg of mastic gum three times daily for three weeks significantly improved stomach pain, pain related to anxiety, and heartburn compared to placebo, a genuinely positive result for symptom relief, though not for H. pylori eradication or structural mucosal repair. (12)
Mastic gum's strongest evidence is the in vitro antibacterial data and the dyspepsia symptom trial. Its human eradication data hasn't caught up to the lab result. See the full comparison with S-methylmethionine for mechanism and safety detail.
L-glutamine
L-glutamine is an amino acid that serves as the primary fuel source for intestinal epithelial cells, and it's commonly discussed for supporting the gut lining generally rather than the stomach specifically. The strongest human trial evidence for this compound is in intestinal permeability, not gastritis: a randomized, double-blind, placebo-controlled trial in patients with postinfectious, diarrhea-predominant IBS found that 5 grams three times daily for eight weeks normalized intestinal permeability (measured by urinary lactulose/mannitol ratio) in the majority of the glutamine group, compared to a small fraction of the placebo group. (13)
That's a genuinely strong result, but it's an intestinal permeability and IBS trial, not a gastric mucosa or gastritis-specific trial the way the SMM, DGL, zinc carnosine, and mastic gum research above is. A 2024 systematic review and meta-analysis of glutamine and gut permeability across 10 trials found no significant effect when pooling all doses together, but did find a significant reduction in permeability at doses above 30 grams per day taken short-term. (14) That's a wide gap from the 15 g/day, 8-week protocol used in the positive IBS trial, which is worth naming directly rather than smoothing over.
L-glutamine is a reasonable option for general gut barrier support, but it doesn't currently have a dedicated gastritis or gastric ulcer clinical trial the way the other four compounds on this list do.
How they compare, at a glance
Five different mechanisms, aimed at different parts of the picture: zinc carnosine works through prostaglandin-independent cytoprotection and antioxidant activity, with the deepest comparative trial data of the group. SMM stimulates mucin production and supports the mucosal lining directly, with evidence spanning acute ulcer healing and chronic gastritis maintenance. DGL increases prostaglandin synthesis and mucus-cell activity, with its strongest data being antibacterial (one specific extract). Mastic gum has laboratory-confirmed antibacterial activity against H. pylori and trial-confirmed dyspepsia symptom relief, though not confirmed human H. pylori eradication. L-glutamine fuels intestinal cells directly and has its strongest evidence in general gut permeability rather than the stomach specifically.
None of these have been tested head-to-head against each other in a single trial. Each comparison above draws on a separate research base, not a shared study design.
Safety notes
All five compounds have shown generally favorable safety records in their available research, with different specific considerations: zinc carnosine's main long-term caution is copper absorption at high doses, SMM's is mild gastrointestinal discomfort on an empty stomach, DGL and mastic gum have not shown significant adverse effects in their published human trials (though both have a smaller volume of long-term human safety data than SMM or zinc carnosine), and glutamine at very high doses (the 30+ g/day range studied in the permeability meta-analysis) hasn't been studied long-term outside clinical supervision.
None of these compounds are a substitute for confirmed H. pylori treatment, which requires antibiotics under medical supervision. If you test positive for H. pylori, that's a conversation for a doctor first, regardless of which supplement is also under consideration. For the complete safety picture on S-methylmethionine specifically, see the side effects guide.
Summary
Five compounds, five different mechanisms. Zinc carnosine has the deepest comparative trial data of the group, including a 258-patient trial against a pharmaceutical comparator. SMM has evidence spanning both acute ulcer healing and chronic gastritis maintenance, plus pharmaceutical use in two countries across more than 70 years. DGL's strongest evidence is antibacterial, tied to one branded extract. Mastic gum has a well-known in vitro antibacterial finding that hasn't yet been confirmed in human eradication trials, alongside a positive short-term dyspepsia symptom trial. L-glutamine's strongest evidence is for intestinal permeability generally, rather than gastritis specifically.
For more on how SMM specifically fits into daily life, see what to eat during a gastritis flare, whether it's safe to combine with a PPI, and how it actually works in the body.
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. Matsukura T, Tanaka H. Applicability of zinc complex of L-carnosine for medical use. Biochemistry (Mosc). 2000;65(7):817-23. link
2. Miyoshi A, Namiki A, Asagi S, Harasawa S, Ooshiba S, Hayakawa K. Clinical Evaluation of Z-103 on Gastric Ulcer: A Multicenter Double-Blind Comparative Study with Cetraxate Hydrochloride. Jpn Pharm Ther. 1992;20:199-223. link
3. Polaprezinc combined with clarithromycin-based triple therapy for Helicobacter pylori-associated gastritis: A prospective, multicenter, randomized clinical trial. link
4. Watanabe T, et al. Augmentative Effects of L-Cysteine and Methylmethionine Sulfonium Chloride on Mucin Secretion in Rabbit Gastric Mucous Cells. 2000. link
5. Cheney G. Rapid Healing of Peptic Ulcers in Patients Receiving Fresh Cabbage Juice. California Medicine. 1949;70(1):10-15. link
6. 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. link
7. Deglycyrrhizinated Licorice (DGL) in Promoting Gastric Mucosal Health. Council for Accreditation in Complementary Health Sciences. link
8. Double-blind trial of deglycyrrhizinated liquorice in gastric ulcer. Gut. 1971. link
9. 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. link
10. Huwez FU, Thirlwell D, Cockayne A, Ala'Aldeen DA. Mastic gum kills Helicobacter pylori. N Engl J Med. 1998;339(26):1946. link
11. Dabos KJ, et al. The effect of mastic gum on Helicobacter pylori: A randomized pilot study. Phytomedicine. 2010. link
12. Dabos KJ, et al. Is Chios mastic gum effective in the treatment of functional dyspepsia? A prospective randomised double-blind placebo controlled trial. J Ethnopharmacol. 2010. link
13. Zhou Q, Verne ML, Fields JZ, Lefante JJ, Basra S, Salameh H, Verne GN. Randomised placebo-controlled trial of dietary glutamine supplements for postinfectious irritable bowel syndrome. Gut. 2019;68(6):996-1002. link
14. Abbasi F, Haghighat Lari MM, Khosravi GR, et al. A systematic review and meta-analysis of clinical trials on the effects of glutamine supplementation on gut permeability in adults. Amino Acids. 2024;56:60. link
*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.