Black Seed Oil (Nigella Sativa) for Weight Loss: The Evidence

Black seed oil may produce a small amount of weight loss, about 1.6 kg in the newest meta-analysis (95% CI -3.03 to -0.15 kg), a review of 31 trials and 2,145 people with metabolic diseases in which about a dozen trials contributed to the weight estimate.^[1] That analysis found no significant effect on waist circumference, and its authors caution that the findings should be read carefully.^[1] The trials are mostly short and differ widely from one another, and none of the evidence shows black seed working anywhere near the scale of a prescription GLP-1 drug.

What the meta-analyses found

Black seed, or Nigella sativa, has been pooled in several reviews. Most report a loss of roughly 1.6 to 2.1 kg against a control, as summarized in the table below, drawn from Namazi 2018,^[6] Mousavi 2018,^[5] Shahinfar 2023,^[4] Karimi 2025^[3] and Musazadeh 2026.^[1] The largest review, Jafari 2025, covered 82 studies and 5,026 participants with doses from 200 to 4,600 mg per day over 1 to 48 weeks. Its abstract says weight and body fat percentage improved but does not give an effect size for weight, so it isn't in the table.^[2]

Those figures need tempering. The spread between trials is very large: an I² of 95.7% in Musazadeh 2026 means most of the variation reflects real differences between studies, so a single pooled number describes them poorly.^[1] The Karimi review of 16 trials in type 2 diabetes found no significant weight effect.^[3] Musazadeh, by contrast, reported that long-term use could help weight and BMI in that same group, but its type 2 diabetes subgroup for weight contained a single trial.^[1] A waist effect is not consistent either: Namazi found one (-3.52 cm), while Mousavi and Musazadeh did not.^[6][5][1]

The Musazadeh paper also isn’t consistent about its own certainty. Its results section and GRADE table rate the weight evidence as high quality, and the table lists an estimate of -2.16 kg from 11 trials rather than the headline -1.59 kg. Its discussion calls the same evidence moderate.^[1] Its authors say that publication bias and sensitivity results mean the weight findings “should be interpreted with caution.” They also note that most trials ran only 4 to 24 weeks and that a loss of about 2 kg falls short of the 5% of body weight usually treated as meaningful.^[1]

What individual trials look like

Individual trials show how small and varied this evidence is. Several lasted only 8 weeks, and one paired the oil with a low-calorie diet in both arms.

• With a low-calorie diet: 90 women with obesity took 3 g per day of oil or placebo for 8 weeks, with 84 finishing. Weight fell 6.0% versus 3.6% (p<0.01).^[7] The placebo group lost weight too, so the gap between groups is about 2.4 percentage points.
• In coronary artery disease: 60 patients took 2 g of oil or sunflower oil for 8 weeks. The abstract reports a 1.82 kg reduction compared with placebo.^[8]
• In type 2 diabetes: a 43-person trial of 1 g per day of oil extract for 8 weeks reported lower BMI and waist circumference (both p<.001).^[9] That is a small trial, and its result sits against the null pooled finding in Karimi 2025.^[3]
• With powdered seed: in a 123-person randomized trial, the abstract describes favorable trends in almost all measures, but they were not statistically significant. Only 39 people in the black seed arm and 34 in the control arm finished.^[11]
• Against lifestyle change or metformin: in 117 people with obesity and prediabetes, 450 mg of oil twice daily for 6 months was statistically similar to metformin 500 mg twice daily on weight and BMI, and not significantly different from a diet and exercise program.^[12] This trial had no placebo arm, and a failure to find a difference does not show the three are equivalent.

One crossover trial is hard to interpret from its abstract. In 45 women with overweight or obesity given 2,000 mg of oil per day, the abstract reports a “considerable increment” in BMI, body weight and waist circumference measures, along with small decreases in fat mass and visceral fat, then concludes that these were overall improvements.^[10] The direction of the weight result is unclear from that wording, so we wouldn’t count this trial as evidence either way on the scale.

The “natural GLP-1” claim rests on rats

Marketing sometimes ties black seed to GLP-1, the hormone that drugs like semaglutide mimic. The closest evidence comes from animals. Thymoquinone, a compound in the seed, raised plasma GLP-1 and reduced excess eating in rats with induced diabetes.^[13] A different rat study, in healthy animals, found that 1,000 mg/kg of black seed for 9 weeks made no significant difference to food intake or weight, and that it increased ghrelin, a hunger hormone.^[14] Neither result tells us what a capsule does to GLP-1 in a person. Our reviews of so-called GLP-1 vitamins and berberine as “nature’s Ozempic” look at similar claims.

For scale, consider STEP 1, a 68-week trial of semaglutide 2.4 mg in adults with overweight or obesity and no diabetes. Using an estimand that counted people regardless of whether they stopped treatment, the difference from placebo was -12.7 kg (95% CI -13.7 to -11.7).^[15] Black seed trials differ in population, length and design, so this is an indirect comparison, but the semaglutide difference is numerically far larger than the roughly 2 kg seen in the black seed reviews.^[1][4] Black seed has not been tested as a replacement for a GLP-1 drug, and we found no randomized trial adding it to one.

Where the evidence looks stronger: glucose and blood pressure

The more consistent signals are in lab values and blood pressure. Musazadeh 2026 reported lower fasting glucose (-18.62 mg/dL), HbA1c (-0.56) and systolic blood pressure (-3.25 mmHg), but no effect on HOMA-IR or insulin. Heterogeneity was again high, at 99.2% for fasting glucose, and the review rated 12 of its 31 trials as high quality.^[1] The authors also found signs of publication bias for fasting glucose and advise caution about the size of that effect, and their GRADE table rates the HbA1c evidence as low quality.^[1] In type 2 diabetes, Karimi 2025 found lower fasting glucose (-21.43 mg/dL), HbA1c (-0.44), total cholesterol (-18.80 mg/dL) and LDL (-19.53 mg/dL).^[3] These are intermediate markers, and the abstracts of these reviews report no hard outcomes such as heart attacks or diabetes complications. Our graded review of supplements used on a GLP-1 puts this kind of evidence in context.

Safety: reassuring averages, a few warnings

Trial data look reasonably reassuring over the short term. Namazi 2018 noted no serious side effects, and Karimi 2025 found no significant change in liver enzymes or creatinine.^[6][3] A 90-day placebo-controlled safety trial of a thymoquinone-rich oil at 200 mg per day in 70 healthy adults found no serious adverse effects, though some of its authors work at the research center of an ingredient company, Akay Natural Ingredients.^[17] That dose is far below the 2 to 3 g per day used in some weight trials,^[7][8] and products vary: that study’s oil contained 5% thymoquinone, versus under 1% in the low-content oils its authors say were studied before.^[17]

Some signals point the other way. A meta-analysis of liver and kidney measures found lower alkaline phosphatase and blood urea nitrogen overall, but doses above 2,000 mg per day raised blood urea nitrogen, and creatinine rose in a small set of adjusted analyses (3 trials, 152 participants).^[16] A published case report described acute kidney injury, rhabdomyolysis and liver toxicity after black seed oil ingestion.^[18] Another described a large hematoma in a man on dual antiplatelet therapy and chemotherapy, with a platelet count of 52 × 10³/µL, after his dose rose to 2,000 mg per day; causality was rated only “possible,” he had several other bleeding risks, and a later 1,000 mg per day dose caused no recurrence.^[19] Case reports cannot establish that a supplement caused the harm, and they cannot show how often it happens, but they justify caution for people with those conditions.