Black seed (Nigella sativa): what the studies show

By the Voltra team · Updated 30 September 2026

What black seed is

Black seed, also called black cumin, habbat al-baraka or Nigella sativa, is a spice and a traditional remedy. The US National Institutes of Health's LiverTox database describes it as "a flowering plant native to Eastern Europe and the Middle East that produces black seeds which are used to produce spice and flavoring of food and have been used in traditional medicine as therapy for a wide variety of conditions" [1]. In the trials below, people took it as powdered seed in capsules or as oil [6] [8].

For many readers black seed also has religious significance. This guide doesn't make or dispute religious claims; it looks only at what clinical trials have measured.

Weight and waist

Difference against placebo or control, as printed in each review's abstract. The 2026 review's own tables give −2.16 kg for weight, not the −1.59 kg in its abstract [6].

That's between about 1.6 and 2.1 kg, in trials that lasted 4 to 24 weeks [6]. The authors of the 2026 review say "the magnitude of these effects was modest and may limit their clinical relevance", and note that a loss of at least 5% of body weight is usually taken as meaningful [6]. They rated their weight evidence as high certainty, but results varied widely between trials, and they say the findings should be read with caution [6]. The waist didn't reliably shrink: one review found a smaller waist, two found no significant change [3] [4] [6].

Blood sugar and HbA1c

A 2022 review pooled 11 trials in 666 people with type 2 diabetes or prediabetes: 7 were in Iran, 2 in India, 1 in Egypt and 1 in Saudi Arabia (calculated from the review's list) [7]. Black seed lowered fasting blood sugar by about 24 mg/dL and HbA1c by about 0.5 percentage points more than the control groups [7]. The review rated that evidence low for fasting sugar and very low for HbA1c, because the trials disagreed a lot and, for HbA1c, because of signs of publication bias [7]. The trials used 0.9 to 5 g a day for 2 to 6 months; that's what the trials used, not a dose to take [7].

The 2026 review found similar drops, about 19 mg/dL in fasting sugar and 0.56 in HbA1c, but no change in insulin or insulin resistance; its authors warn that signs of publication bias mean the fasting sugar result should be read with caution [6]. A 2025 review of reviews on herbal medicines for type 2 diabetes found that the black seed review it assessed gave only before-and-after changes within each group, not comparisons between groups, so it couldn't grade the evidence; it said black seed's safety can't be determined from the available evidence [8].

Don't swap your diabetes medicines for it: Saudi Arabia's National Center for Complementary and Alternative Medicine (NCCAM) says medicines for chronic conditions such as diabetes and high blood pressure must not be stopped without medical supervision [25]. Our guide to prediabetes and insulin resistance covers what lowers blood sugar with better evidence.

Cholesterol and blood pressure

In the 2022 review of people with diabetes, total cholesterol fell by about 24 mg/dL and LDL cholesterol by about 20 mg/dL, while triglycerides and HDL didn't change significantly [7]. It rated the evidence low for LDL and very low for total cholesterol [7]. Six earlier meta-analyses also found LDL lower [2].

For blood pressure, two reviews found systolic pressure about 3 mmHg lower and diastolic about 2.7 mmHg lower than with placebo [9] [6]. The authors of the 2026 review note that a drop of 5 mmHg is usually considered the threshold for a meaningful improvement [6].

Exercise and muscle

There's almost no research on black seed for training. A 2023 review from Saudi Arabia that looked for studies combining black seed with exercise found two in people and two in animals [10]. In one, 20 inactive, overweight women in Iran did aerobic training for 8 weeks with black seed capsules or a placebo, and 16 finished. Fitness (VO2 max) rose in both groups; the only differences between the groups were in LDL and HDL cholesterol [11]. In a trial with 54 military cadets, a ration bar with black seed plus arginine and beta-alanine improved sprint power over two weeks but not VO2 max; with three active ingredients, black seed's own effect can't be separated [12].

A 2025 review of 82 trials listed skeletal muscle mass among the measures that improved, but its abstract gives no figure or number of trials, and we couldn't read the full paper [13]. No trial we found shows that black seed by itself builds muscle or improves performance.

How good is the evidence?

An overview of 20 meta-analyses published between 2013 and 2021 rated the methods of one moderate, four low and 15 critically low [2]. Of the 110 results it graded, 5 were moderate certainty, 17 low and 88 very low, and none high. Its conclusion: "The clinical efficacy of N. sativa requires confirmation in high-quality, large-sample, randomized controlled trials." [2]

The trials were short, 4 to 24 weeks in the 2026 review [6]. The reviews often didn't report who funded the individual trials [2]. Industry links aren't always obvious: a 2022 safety trial of a branded black seed oil in 70 healthy adults in India reported no serious side effects over 90 days, but four of its six authors work for the company that makes the oil, which prepared the study product and approved the protocol [14].

Side effects, and who should be careful

In the trials, the side effects reported were mainly stomach pain, diarrhoea, nausea and vomiting, and none were serious, but only five of the 20 reviews reported on side effects at all [2]. LiverTox says: "Black cumin is well tolerated, is generally recognized as safe and has not been associated with serum enzyme elevations during therapy nor implicated in cases of clinically apparent liver injury." [1]

• Kidneys. Doctors in Turkey reported acute kidney failure associated with black seed in a person with diabetes (we could read only the report's title) [15], and in 2024 a case of acute kidney injury, muscle breakdown (rhabdomyolysis) and liver damage after taking black seed oil by mouth [16]. Single cases can't show how common a problem is.
• Skin. NIH's LactMed database says: "Black seed oil can cause allergic contact dermatitis." [17] In France, three women had severe blistering reactions that spread beyond where they had applied the oil, with more than 15% of their skin detached [18]. A 2026 US report describes a similar reaction in a man who swallowed a supplement combining black seed oil with oregano oil [19].
• Diabetes medicines. In rats, black seed oil raised blood levels of the diabetes drug gliclazide, and in healthy rats it increased the drug's sugar-lowering effect by up to 50% [20]. We found no human study of this. A 2025 review advises careful monitoring for low blood sugar when herbal medicines are taken with diabetes drugs [8].
• Other medicines. In four healthy volunteers in Riyadh, a week of black seed slowed the breakdown of a test drug (dextromethorphan) by two liver enzymes, CYP2D6 and CYP3A4; the authors say it could interact with other drugs these enzymes break down [21]. In rabbits it cut blood levels of the transplant drug cyclosporine (AUC) by 55.9% [22]. And a report from Iran describes a large bleed under the skin in a man taking black seed oil with two antiplatelet drugs and chemotherapy; the link was rated possible [23].
• Pregnancy and breastfeeding. We found no trials in pregnancy. For breastfeeding, LactMed says: "No data exist on the excretion of any components of black seed into breastmilk or on the safety and efficacy of black seed in infants." [17] NCCAM lists children and pregnant and breastfeeding women among those who should ask a doctor or pharmacist before using herbal products [24].

NCCAM also warns that herbal products may increase the risk of bleeding or drowsiness, or affect blood pressure or blood sugar, and asks people to tell their doctor or pharmacist about every herbal product they use [24]. There's no European Union herbal monograph for black seed: it isn't on the European Medicines Agency's list of herbal substances assessed [29].

Rules in Saudi Arabia, the UAE and Kuwait

We found no Gulf warning about adulterated or fake black seed products. NCCAM warns more generally against buying herbal mixtures from unlicensed sellers, because some products may contain harmful or contaminated substances [26], and advises checking that a product is registered or listed with the Saudi Food and Drug Authority [24]. Our guide to which supplements are worth taking covers the better-studied options.

In Voltra

If you take black seed, you can log it in the Eat tab like any food, by searching for it or describing it, and the Coach can answer questions using what you've logged.

Frequently asked

Sources

1. National Institute of Diabetes and Digestive and Kidney Diseases (NIH) (2023). LiverTox: Black Cumin Seed (updated 27 April 2023). Public domain. Summary, read from its PubMed record (PMID 37184195).
2. Li Z, Wang Y, Xu Q, et al. (2023). Nigella sativa and health outcomes: an overview of systematic reviews and meta-analyses. Front Nutr 10:1107750. 20 meta-analyses published 2013–2021. Funded by the National Natural Science Foundation of China.
3. Namazi N, Larijani B, Ayati MH, Abdollahi M (2018). The effects of Nigella sativa L. on obesity: a systematic review and meta-analysis. J Ethnopharmacol 219:173–181. Abstract.
4. Mousavi SM, Sheikhi A, Varkaneh HK, et al. (2018). Effect of Nigella sativa supplementation on obesity indices: a systematic review and meta-analysis of randomized controlled trials. Complement Ther Med 38:48–57. Abstract.
5. Shahinfar H, Jayedi A, Torabynasab K, et al. (2023). Comparative effects of nutraceuticals on body weight in adults with overweight or obesity: a systematic review and network meta-analysis of 111 randomized clinical trials. Pharmacol Res 196:106944. Abstract.
6. Musazadeh V, Jahangir M, Mahmoudinezhad M, et al. (2026). The effect of Nigella sativa supplementation on cardiometabolic health in patients with metabolic diseases: a GRADE-assessed systematic review and meta-analysis. Endocrinol Diabetes Metab 9(2):e70207. Abstract and full text. 31 trials in people with metabolic diseases, 4 to 24 weeks. No funding reported.
7. Saadati S, Naseri K, Asbaghi O, et al. (2022). Nigella sativa supplementation improves cardiometabolic indicators in population with prediabetes and type 2 diabetes mellitus: a systematic review and meta-analysis of randomized controlled trials. Front Nutr 9:977756. Abstract and full text. 11 trials, 666 people with type 2 diabetes or prediabetes.
8. Li E, Maunder A, Liu J, et al. (2025). The efficacy and safety of herbal medicines for glycaemic control and insulin resistance in individuals with type 2 diabetes: an umbrella review. BMC Complement Med Ther 25:341. Abstract and full text.
9. Kavyani Z, Musazadeh V, Safaei E, et al. (2023). Antihypertensive effects of Nigella sativa supplementation: an updated systematic review and meta-analysis of randomized controlled trials. Phytother Res 37(8):3224–3238. Abstract.
10. Alyami HH, Al-Hariri MT (2023). Synergistic effects of Nigella sativa and exercise on diabetic profiles: a systematic review. Diabetes Ther 14(3):467–478. Abstract and full text. Authors at Imam Abdulrahman Bin Faisal University, Dammam.
11. Farzaneh E, Nia FR, Mehrtash M, Mirmoeini FS, Jalilvand M (2014). The effects of 8-week Nigella sativa supplementation and aerobic training on lipid profile and VO2 max in sedentary overweight females. Int J Prev Med 5(2):210–216. Full text. 20 women randomised in Kerman, Iran; 16 finished.
12. Hadi S, Miryan M, Soleimani D, et al. (2021). The effect of food ration bar enriched with β-alanine, L-arginine, and Nigella sativa on performance and inflammation following intense military training: a double-blind randomized clinical trial. Food Sci Nutr 9(7):3512–3520. Abstract and full text. 54 cadets, Iran.
13. Jafari A, Mardani H, Faghfouri AH, et al. (2025). Does Nigella sativa supplementation improve cardiovascular disease risk factors? A comprehensive GRADE-assessed systematic review and dose-response meta-analysis of 82 randomized controlled trials. Pharmacol Res 219:107882. Abstract; the full text was not accessible to us.
14. Thomas JV, Mohan ME, Prabhakaran P, Das SS, Maliakel B, Krishnakumar IM (2022). A phase I clinical trial to evaluate the safety of thymoquinone-rich black cumin oil (BlaQmax®) on healthy subjects. Toxicol Rep 9:999–1007. Full text, including the declaration of competing interest. 70 healthy adults, India.
15. Arslan E, Sayin S, Demirbas S, et al. (2013). A case study report of acute renal failure associated with Nigella sativa in a diabetic patient. J Integr Med 11(1):64–66. Title only; no abstract.
16. Sener K, Cakir A, Yesiloglu O, Altug E, Guven R, Korkut S (2024). Rhabdomyolysis and acute kidney injury after consumption of black seed oil. Toxicon 245:107787. Abstract. Single case, Turkey.
17. National Institute of Child Health and Human Development (NIH) (2025). Drugs and Lactation Database (LactMed): Black Seed (updated 15 July 2025). Public domain. Summary, read from its PubMed record (PMID 30000936).
18. Gaudin O, Toukal F, Hua C, et al. (2018). Association between severe acute contact dermatitis due to Nigella sativa oil and epidermal apoptosis. JAMA Dermatol 154(9):1062–1065. Abstract. Three cases, France.
19. Chu B, Kinariwalla N, Elco CP, Seo SJ (2026). Bullous cutaneous reaction mimicking Stevens-Johnson syndrome due to Nigella sativa supplement ingestion. JAAD Case Rep 75:339–342. Full text. Single case, USA.
20. Adiwidjaja J, Sasongko L (2021). Effect of Nigella sativa oil on pharmacokinetics and pharmacodynamics of gliclazide in rats. Biopharm Drug Dispos 42(8):359–371. Abstract. Study in rats.
21. Al-Jenoobi FI, Al-Thukair AA, Abbas FA, et al. (2010). Effect of black seed on dextromethorphan O- and N-demethylation in human liver microsomes and healthy human subjects. Drug Metab Lett 4(1):51–55. Abstract. Four healthy volunteers, King Saud University, Riyadh.
22. Al-Jenoobi FI, Al-Suwayeh SA, Muzaffar I, et al. (2013). Effects of Nigella sativa and Lepidium sativum on cyclosporine pharmacokinetics. Biomed Res Int 2013:953520. Abstract. Study in rabbits.
23. Arab A, Ramezaninejad S, Salehifar E (2026). Extensive subcutaneous hematoma in a patient receiving Nigella sativa oil, dual antiplatelet therapy, and oxaliplatin-based chemotherapy: a case report. Hosp Pharm (online 31 August 2026). Abstract. Single case, Iran.
24. المركز الوطني للطب البديل والتكميلي، وزارة الصحة السعودية (٢٠٢٦). التفاعلات بين المنتجات العشبية والأدوية (٦ سبتمبر ٢٠٢٦). In Arabic.
25. المركز الوطني للطب البديل والتكميلي، وزارة الصحة السعودية (٢٠٢٦). مفاهيم خاطئة عن الطب البديل والتكميلي وممارساته (١٢ أغسطس ٢٠٢٦). In Arabic.
26. المركز الوطني للطب البديل والتكميلي، وزارة الصحة السعودية (٢٠٢٦). الحذر من خلطات عشبية مجهولة قد تحتوي على مواد ضارة أو ملوثة (١٠ مايو ٢٠٢٦). In Arabic.
27. الهيئة العامة للغذاء والدواء (٢٠٢٢). جدول رقم (١): اللوائح الفنية الخليجية الغذائية المعتمدة (١٧ فبراير ٢٠٢٢)، البند ١٨: SFDA.FD GSO 643:2021. In Arabic and English. Item 18, in force from 1 June 2022.
28. Saudi Food and Drug Authority (2026). Herbal drugs list, searched for “Nigella” and “black” (accessed 30 September 2026). Includes products named NIGELLA and Cumin Mar Blackcumin oil.
29. European Medicines Agency, Committee on Herbal Medicinal Products (2026). Overview of assessment work: priority list (EMA/HMPC/561868/2021, last update July 2026). Black seed (Nigella) is not on the list.

Sources checked on 30 September 2026.

Log your food and training with Voltra. Free to download; the yearly plan starts with a 7-day free trial. Works fully in English and Arabic.

Related

Which supplements are worth taking?Berberine for weight loss: is it "Nature's Ozempic"?Prediabetes and insulin resistance: the numbers, and what can reverse itAshwagandha for stress and sleep: what the evidence shows