Cloves: a famous spice that human trials have barely touched

Clove turns up on lists of spices said to lower blood sugar. A 2024 meta-analysis of herbs and spices in type 2 diabetes kept 77 studies and still found too few clove trials to analyze clove at all, so the honest answer is that it has not been tested enough to judge. In that same review, black cumin, cinnamon and ginger lowered fasting glucose by 17 to 27 mg/dL in people with type 2 diabetes. Clove is missing from that list for lack of trials, which says nothing either way about whether it works. The human trials we did find tested toothpaste. In 150 adults with plaque and inflamed gums, a paste that combined clove with five other herbs, zinc and fluoride cut plaque by 23.5% over 6 months against plain fluoride paste. With six botanicals in the tube, the share owed to clove cannot be separated, and brushing it on teeth is a different exposure from eating it.

The numbers, per 3.5 oz (100 g)

How much is actually in it

• Spice composition depends on origin: a 2024 systematic review of 50 studies found Indian cloves high in iron, about 17.87 mg/kg, while some African and European spices exceeded lead and cadmium limits. — Culinary spices and herbs from worldwide markets, 50 peer-reviewed studies (n = 50 studies) Evidence C source
  Iron in Indian cloves and ajwain 17.87 plus or minus 8 mg/kg; no non-carcinogenic risk from Cd, Ni, Cu except chamomile in Turkey
• Ground cloves are dense in fiber, vitamin K and iron per 3.5 oz (100 g), though a typical pinch of under 1 g supplies little of any of them. — USDA reference record for ground cloves Evidence E source
  Per 100 g: fiber 33.9 g (121% DV), vitamin K 141.8 mcg (118% DV), iron 11.83 mg (66% DV)
• The UK table gives dried cloves 5.6 mg iron per 3.5 oz (100 g), about half the USDA figure of 11.83 mg, alongside 730 mg calcium and 8.5 mg manganese. — CoFID reference record for dried cloves Evidence E source
  Per 100 g: iron 5.60 mg, calcium 730 mg, manganese 8.50 mg, magnesium 260 mg, potassium 1100 mg, fat 20.1 g

What it does to your health

• In a 12-week randomized trial of 70 adults, a herbal toothpaste containing clove lowered salivary LDH by 9.5 to 15.4% and plaque by 6.4 to 16.2% versus a control paste. — 70 adults aged 20 to 59, brushing for 12 weeks (n = 70) Evidence B source
  Salivary LDH -9.5 to -15.4%, plaque -6.4 to -16.2%, gingivitis -8.2 to -23.8% versus control (p < 0.05)

What people believe that the data does not support

• Clove is often sold as a blood sugar spice, but in a 2024 meta-analysis of 45 trials only cinnamon, turmeric, ginger, black cumin and saffron lowered fasting glucose in type 2 diabetes. — Adults with type 2 diabetes, 45 interventional studies pooled (n = 45 studies) Evidence A source
  Fasting glucose fell by about 17 to 27 mg/dL with black cumin, cinnamon and ginger; clove not among the spices with a pooled effect
• Clove's oral health reputation rests on multi-ingredient products: a toothpaste with clove plus five other herbs, zinc and fluoride cut plaque by 23.5% over 6 months versus fluoride paste in 150 adults. — Adults with plaque index above 1.5 and gingival index above 1.0, brushing twice daily for 6 months (n = 150 completers (72 test, 78 control)) Evidence B source
  Plaque -23.5%, gingival index -25.6%, bleeding index -73.3% versus fluoride toothpaste at 6 months

Who this works differently for

• People allergic to balsam of Peru may react to clove: 5 of 29 such patients reacted on patch testing to clove, Jamaica pepper or cinnamon, and the authors conclude that swallowed flavorings might cause systemic contact reactions in some. — 29 patients with delayed-type allergy to balsam of Peru, 22 given oral challenges (n = 29) Evidence C source
  Patch test positive to clove, Jamaica pepper or cinnamon in 5 of 29; palmar vesicles rose 30-280% after active challenge in 8 of 22
• Clove oil is not the spice: a 15-month-old developed fulminant liver failure after swallowing 2 tsp (10 ml) of clove oil, and recovered after intravenous N-acetylcysteine. — One 15-month-old boy, plus a UK national poisoning database 1994-1999 (n = 1) Evidence D source
  ALT above 13,000 U/l at 24 h; 14-fold rise in aromatherapy home accidents 1994-1999

What is still unknown

• A 2024 meta-analysis of spices in type 2 diabetes screened 6958 records and kept 77 studies, yet found too few clove trials to analyze clove at all. — Adults with type 2 diabetes in interventional studies of 12 Mediterranean herbs and spices, literature to September 2023 (n = 77 studies in review, 45 in meta-analysis, 0 on clove) Evidence A source
  No pooled estimate for clove: not enough studies on fasting glucose, HbA1c or insulin

The bottom line

A second trial of the same multi-herb paste, in 70 adults over 12 weeks, lowered plaque by 6.4 to 16.2% against a control paste, and again the clove part of that effect is unknown. On paper ground cloves look dense. The USDA record lists 33.9 g of fiber, 141.8 mcg of vitamin K and 11.83 mg of iron per 3.5 oz (100 g), from a single record with no spread across samples. A recipe uses a pinch, far less than 100 g, so you get little of any of them. The sources also disagree on iron. The UK table gives dried cloves 5.6 mg per 3.5 oz (100 g), about half the USDA figure, and a review of market surveys put Indian cloves and ajwain together at about 17.87 mg per kg, a gap that reflects sample, origin and method. This page has no separate safety block. The two findings that bear on safety sit in the section on who this works differently for. Among 29 people with delayed allergy to balsam of Peru, 5 reacted on patch testing to clove, Jamaica pepper or cinnamon, tested together so clove alone was not isolated, and in 8 of 22 given the spices to swallow, blisters on the palms increased. The authors judged that avoiding flavorings brings questionable benefit. Clove oil is a separate product from the spice. In one case report a 15-month-old developed liver failure after swallowing 2 tsp (10 ml) of the oil and recovered after intravenous N-acetylcysteine, and a UK poisoning database showed a 14-fold rise in home accidents with aromatherapy products from 1994 to 1999.

Sources

1. clv-r5-06 · Systematic review
   Indian spices like cloves and Ajwain seeds exhibited high levels of iron (17.87 ± 8 mg/kg) and calcium (1353 ± 10 mg/kg). African and European spices showed regional disparities, with some exceeding permissible Pb and Cd limits.
   Environ Pollut, 2024 · checked 2026-10-02
2. clv-r5-08 · USDA FoodData Central, dataset
   Spices, cloves, ground (FDC 171321, SR Legacy, Spices and Herbs): fiber 33.9 g per 100 g = 121% DV; vitamin K 141.8 ug = 118% DV; iron 11.83 mg = 66% DV; Foundation samples 0
   USDA FoodData Central, SR Legacy, FDC 171321 Spices, cloves, ground, 2019 · checked 2026-10-02
3. clv-r5-09 · CoFID 2021, dataset
   CoFID 13-816 Cloves, dried (group H): Iron 5.60 mg; Calcium 730 mg; Manganese 8.50 mg; Magnesium 260 mg; Potassium 1100 mg; Fat 20.1 g; Protein 6.0 g; Water 6.9 g per 100 g
   CoFID 2021, Public Health England, OGL v3.0, code 13-816 Cloves, dried · checked 2026-10-02
4. clv-r5-04 · Randomized controlled trial
   The test demonstrated reductions in LDH of 9.5-15.4% over the study period in comparison to the control representing statistically significant effects (p < 0.05). The test also demonstrated reductions in dental plaque that ranged between 6.4 and 16.2% over the study period and gingivitis reductions that ranged between 8.2 and 23.8% representing statistically significant results (p < 0.05).
   Clin Oral Investig, 2021 · checked 2026-10-02
5. clv-r5-02 · Meta-analysis
   Our results showed that cinnamon, turmeric, ginger, black cumin, and saffron significantly improved the fasting glucose levels in T2DM subjects. The most significant decreases in fasting glucose were achieved after supplementation with black cumin, followed by cinnamon and ginger, which achieved a decrease of between 27 and 17 mg/dL.
   Nutrients, 2024 · checked 2026-10-02
6. clv-r5-03 · Randomized controlled trial
   In comparison with the control, the test demonstrated reductions in 23.5%, 25.6%, and 73.3% for dental plaque, gingival index and bleeding index outcomes, respectively, at the final visit.
   Int J Dent Hyg, 2021 · checked 2026-10-02
7. clv-r5-05 · Double-blind placebo-controlled challenge
   Positive reactions to balsam of Peru were seen in 17 patients, and to clove, Jamaica pepper or cinnamon in 5. ... It is concluded that ingested flavoured foods might cause systemic contact reactions in some patients with allergy to balsam of Peru, but the benefits of a flavour-avoiding diet are questionable in all of them.
   Contact Dermatitis, 1995 · checked 2026-10-02
8. clv-r5-07 · Case report
   We present a 15-month-old boy who developed fulminant hepatic failure after ingesting 10 ml of clove oil. ... Analysis of a national database revealed a 14-fold increase in home accidents related to aromatherapy from 1994-1999.
   Janes SE et al., European Journal of Pediatrics, 2005 · checked 2026-10-02
9. clv-r5-01 · Meta-analysis
   Finally, only five out of the twelve aromatic herbs and spices were investigated; for the remaining ones (clove, parsley, thyme, black pepper, rosemary, basil, and oregano), not enough studies were found on the glycemic profile in T2DM subjects.
   Nutrients, 2024 · checked 2026-10-02