Black seed oil

A 2022 review of 11 trials (666 people with type 2 diabetes or prediabetes, 9 trials using the oil at 0.9 to 5 g a day for 2 to 6 months) found fasting glucose about 24 mg/dL (1.3 mmol/L) lower and HbA1c about 0.54 percentage points lower than control, but rated the certainty low and very low because results varied widely and smaller positive studies may have been over-published. Seven of the 11 trials were from Iran.

A 2026 review of 31 trials (2,145 people with metabolic diseases) found similar falls in fasting glucose and HbA1c, but no change in insulin or insulin resistance.^1,2

A 2020 review of 50 trials found lower total cholesterol, LDL cholesterol and triglycerides with black seed than with control. In people with type 2 diabetes, the 2022 review found total cholesterol about 24 mg/dL (0.6 mmol/L) and LDL about 20 mg/dL (0.5 mmol/L) lower, with no significant change in triglycerides or HDL; it rated the LDL evidence low certainty because the trials disagreed a lot.^3,1

The 2026 review pooled systolic pressure 3.3 mmHg and diastolic 2.8 mmHg lower than control, but the trials varied hugely (especially for diastolic pressure, which fell only in some subgroups), and the authors say an effect of about 2 to 3 mmHg may be too small to matter clinically. These were people with diabetes, fatty liver or metabolic syndrome, mostly not people being treated for high blood pressure.²

A 2024 review found seven or eight small trials (318 people in all, published 2003 to 2023, 2 to 8 weeks) and reported more people improving and lower nasal symptom scores than with control, with side effects similar in both groups.

The trials used different things (nasal drops, oil or ground seed by mouth, and one Chinese herbal mix that also contained liquorice), most did not describe how allocation was concealed, and the review's own tables and text disagree in places. The authors call for larger, better-designed trials.⁴

A 2021 review of 4 trials (187 people, 4 weeks to 3 months) found better Asthma Control Test scores and FEV1 (a lung-function measure) with black seed added to usual care, but no change in peak flow. The trials were small and mixed: one gave oil capsules of 500 mg twice daily to 80 adults, one was in children and one used a boiled seed extract. It is not a replacement for inhalers.⁵

A 2022 review found 14 skin studies (8 from Iran), mostly topical oil, and only 4 could be pooled. Single small trials stand out: in 60 people with hand eczema, a Nigella ointment improved severity and quality of life about as much as the steroid betamethasone over 4 weeks, and better than a plain moisturiser.

In 60 people with acne, a 1% oil gel twice daily cut comedones and papules over 8 weeks versus placebo gel; in 52 people with vitiligo, the oil shrank lesions a little more than fish oil over 6 months. None has been repeated independently.^6,7