Benefits
Digestive symptom scores with an equal celery seed and ajwain blend
In a placebo-controlled trial of 150 adults with recurring indigestion, capsules of an equal celery seed and ajwain mix (two 500 mg capsules a day for 4 weeks) lowered overall symptom severity more than placebo, with less pain, burning, fullness, early fullness, bloating, belching and nausea. Vomiting did not differ. It was a two-herb blend.
Bloating and belching with an ajwain, ginger and black pepper blend
In 106 adults with recurring bloating, a three-herb capsule of ajwain seed, ginger and black pepper (500 mg three times a day for 2 weeks) reduced bloating frequency and severity, belching and stomach rumbling more than placebo or the anti-gas drug dimethicone, and the gap lasted 8 weeks after stopping. Early fullness did not differ. 84 people finished.
Abdominal pain and bloating with a Shirazi thyme and ajwain capsule
In a three-arm trial of 150 adults with irritable bowel symptoms, a capsule combining Shirazi thyme (Zataria multiflora) and ajwain for 4 weeks reduced abdominal pain, bloating, reflux symptoms and fatigue more than placebo or the antispasmodic drug mebeverine. The abstract does not give the dose or how many people finished.
Digestive comfort with a capsule of ajwain, dill and Shirazi thyme oils
A soft-gel holding ajwain, dill and Shirazi thyme essential oils (about 108 mg of ajwain oil a day for 2 weeks) gave higher response rates than omeprazole in 64 adults with recurring indigestion, and higher improvement rates than hyoscine in 64 adults with irritable bowel symptoms. Neither trial had a placebo group, and the product is under a patent application.
Ajwain seed extract on its own in an 8-week placebo-controlled trial
In 55 adults with fatty liver, three 500 mg capsules a day of ajwain seed water extract plus lifestyle advice for 8 weeks was followed by lower indigestion severity and lower levels of the liver enzyme ALT in the ajwain group. The English abstract does not say whether these changes differed from placebo; the one result it clearly compares between groups, AST, did not differ, and the paper is not indexed in PubMed.
Short-term airway response to a single dose of boiled seed extract
In people with asthma, a single oral dose of boiled ajwain extract raised lung function readings by about 23 to 32% within 90 to 120 minutes, while placebo produced no significant rise. The rise was smaller than with the drug theophylline. The abstract does not give the number of people, and this was a one-dose test, not daily use.
Stomach lining and gut muscle effects in rats and isolated tissue (animal study)
In rats, ajwain essential oil given by mouth cut alcohol-induced stomach lining damage in a dose-dependent way, and a seed extract reduced the liver enzyme rise caused by liver toxins. In isolated gut tissue the extract relaxed muscle like a calcium channel blocker. These are animal and lab results only.
Mechanism of action
Thymol-rich essential oil
Ajwain fruits yield about 2 to 5% essential oil. In ten Iranian samples, five had thymol as the main component (35 to 63% of the oil) while others were dominated by p-cymene or gamma-terpinene, so thymol content varies by source. One trial oil measured 51% thymol. This overlaps the 10 to 64% thymol reported for thyme oil.
Thymol reaches the blood as thymol sulfate
No absorption study has used ajwain itself. In 12 volunteers given a thyme tablet with 1.08 mg thymol, free thymol was not found in blood, but thymol sulfate peaked about 2 hours later, had a half-life of about 10 hours and was detectable up to 41 hours, which suggests how thymol from ajwain is likely handled.
Gut muscle and stomach acid in lab and animal work
A seed extract relaxed isolated rabbit jejunum by blocking calcium entry, much like verapamil. In anesthetized rats, a water extract perfused into the stomach raised acid output almost fourfold, and atropine reduced this rise, pointing partly to a cholinergic route. In rats, the oil and its thymol reduced alcohol damage to the stomach lining, and docking work suggested thymol may bind the stomach acid pump.
Platelet effects in lab tests
An ether extract of ajwain inhibited aggregation of human platelets in test tubes, mostly against arachidonic acid, by cutting thromboxane production through a direct action on cyclooxygenase. This has not been measured in people taking ajwain by mouth.
Clinical trials
Randomized, double-blind, three-arm trial at Kerman University of Medical Sciences, Iran, part of a PhD thesis supported by the university. Capsules of an equal mix of celery seed (Apium graveolens) and ajwain, two 500 mg capsules a day for 4 weeks, versus cornstarch placebo or omeprazole 20 mg, with 4 more weeks of follow-up. Outcomes were the severity and frequency of eight dyspepsia symptoms: pain, burning, early fullness, fullness, bloating, belching, nausea and vomiting. (Azimi et al. 2017, Avicenna J Phytomed)
150 adults with functional dyspepsia by Rome III criteria (50 per group); 49, 43 and 45 completed in the blend, placebo and omeprazole groups.
Overall symptom severity and frequency fell more with the blend than with placebo or omeprazole by week 4 and kept falling through follow-up. The blend did better than placebo on seven of the eight symptoms; vomiting did not differ from placebo. Ajwain made up half of a two-herb blend, so its own share of the effect is unknown.
Double-blind, randomized, three-arm trial in Babol, Iran (registered IRCT2015100324327N1, funded by Babol University of Medical Sciences) of KAASER, a capsule of ajwain seed, ginger rhizome and black pepper, 500 mg three times a day for 2 weeks, versus placebo or the anti-gas drug dimethicone, in adults with functional bloating; follow-up to week 10. Primary outcomes were bloating frequency and severity. Neither the abstract nor the registry gives each herb's share. (Mahmoudpour et al. 2019, J Integr Med)
106 adults aged 20 to 50 with the functional complaint named in the study details; 84 completed the study.
Both primary outcomes improved more with the herbal capsule than with dimethicone or placebo (P < 0.001), as did belching, defecation frequency and stomach rumbling (P = 0.03), and the differences lasted 2 and 8 weeks after stopping. Early fullness did not differ among the three groups. The herb shares are unknown, so the result cannot be credited to ajwain alone.
Randomized, three-arm parallel trial at Kerman University of Medical Sciences, Iran, of a capsule combining Zataria multiflora (Shirazi thyme) and ajwain for 4 weeks, versus placebo or the antispasmodic drug mebeverine, with 2 weeks of follow-up, in adults with irritable bowel syndrome. The abstract reports between-group results for pain, bloating, reflux symptoms and fatigue; its conclusion also names constipation and bowel movements without figures. It gives neither the dose, the herb ratio nor the funding. (Jamalizadeh et al. 2022, Explore (NY))
150 adults, 50 per group, with the diagnosis named in the study details.
After 4 weeks, abdominal pain and two other main symptoms fell more with the herbal capsule than with placebo or mebeverine (P < 0.05), and fatigue fell more too. The abstract gives no completion figures. Two herbs were combined, Shirazi thyme named first, so ajwain's share of the effect is unknown.
Randomized, double-blind, parallel trial in Bandar Abbas, Iran, funded by the Hormozgan Province Science and Technology Park; the product is under a patent application. A 250 mg soft-gel of Zataria multiflora (28.8%), dill (21.6%) and ajwain (21.6%) oils in sunflower oil, twice daily for 2 weeks, versus omeprazole 20 mg daily. (Bordbar et al. 2020, Gastroenterol Res Pract)
64 adults with functional dyspepsia by Rome III criteria randomized (32 per group); 4 were excluded for lack of cooperation.
Adequate response was 78.3% vs 36.4% for fullness-type symptoms and 73.7% vs 40.9% for pain-type symptoms with the oil capsule vs omeprazole, and symptom scores fell more. Side effects were one case each of bad taste and stomach pain. With no placebo arm, this compares the blend with omeprazole over 2 weeks and does not show how it compares with no treatment. Ajwain oil was a smaller share of the capsule than Shirazi thyme oil.
Double-blind randomized trial at Shahed University, Tehran, of three 500 mg capsules a day of ajwain seed water extract or placebo for 8 weeks, both with lifestyle advice. Only the abstract is in English; the journal is not indexed in PubMed and the abstract does not state funding. (Shafiezadeh et al. 2019, J Islam Iran Tradit Med)
55 adults with non-alcoholic fatty liver disease (27 ajwain, 28 placebo), most aged 30 to 50.
The abstract reports that ALT, liver fat grade and indigestion severity (P = 0.025) improved in the ajwain group, without saying clearly whether these were between-group tests. AST fell in both groups with no difference between them (P = 0.098), and weight fell in both groups. This is the only controlled trial found of ajwain taken alone for digestion.
Animal study from Tehran University of Medical Sciences: rats received ajwain essential oil (31.25 to 500 mg/kg), thymol, p-cymene or gamma-terpinene by gavage with 80% ethanol, followed by stomach tissue scoring and a computer docking analysis. (Eftekhari et al. 2019, Daru)
Laboratory rats with ethanol-induced stomach lesions; no people were studied.
The oil, which was 37% p-cymene, 35% gamma-terpinene and 21% thymol, reduced lesions in a dose-dependent way, with 98.6% inhibition at 500 mg/kg. Thymol alone gave 79.4% inhibition at 100 mg/kg and was the most potent of the three main components. Docking suggested thymol may bind the stomach acid pump (H+/K+ ATPase). Rat results do not show effects in people.