Black Seed Oil

Last reviewed October 2026 · Based on 22 studies

Bottom line

Several meta-analyses of trials suggest black seed oil modestly lowers fasting blood sugar, LDL cholesterol and systolic blood pressure. The evidence is limited: the trials are mostly small and short, use different forms and doses, and measure blood tests rather than heart attacks, strokes or diabetes complications. Safety data are thin; the trials that reported side effects found mostly mild stomach upset.

What it helps with

Lowers blood sugar — Benefit, evidence grade C (Limited). Several meta-analyses of 16 to 31 trials found lower fasting glucose and HbA1c; downgraded for surrogate markers and for different forms and doses.
Lowers LDL ('bad') cholesterol — Benefit, evidence grade C (Limited). Meta-analyses of 16 to 50 trials found LDL falls; downgraded for a surrogate marker and for different forms and doses.
Raises HDL ('good') cholesterol — Mixed results, evidence grade C (Limited). Reviews disagree (one found a rise, one found no change) and single trials show no change; HDL is a surrogate marker.
Lowers blood pressure — Benefit, evidence grade C (Limited). Meta-analyses of 11 to 31 trials found about 3 mmHg lower systolic pressure, with high variation between trials; downgraded for inconsistency and for a surrogate outcome.

What it is

Black seed (Nigella sativa) is a plant whose seeds are used as a spice and in traditional medicine. Its main active compound is thymoquinone, which is abundant in the volatile oil fraction [1]. Trials used standardised seed oil, ground seed powder, seed extracts and a honey-based mix [2][3][4].

How it might work

The trial authors propose antioxidant effects. In a one-year trial of 114 people with type 2 diabetes, black seed raised antioxidant measures such as total antioxidant capacity and glutathione compared with placebo [5]. A review of mostly animal models also proposed effects on insulin secretion and glucose absorption [6].

What the research says

Blood sugar. Three meta-analyses of 16 to 31 trials found lower fasting blood sugar and HbA1c. One review of 16 trials in type 2 diabetes found fasting blood sugar about 21 mg/dL lower and HbA1c about 0.44 points lower [7]. A 2026 review of 31 trials found fasting blood sugar about 19 mg/dL lower and HbA1c about 0.56 points lower [8]. A 2019 review of 17 trials found fasting blood sugar about 10 mg/dL lower [9]. In a one-year trial of 114 people with type 2 diabetes on usual medicines, fasting blood sugar fell from 195 to 172 mg/dL in the black seed group, while the placebo group stayed at 180 [5]. In a three-month open-label trial of newly diagnosed people, black seed oil capsules lowered blood sugar less than metformin [10].

Cholesterol. LDL cholesterol fell by about 14 mg/dL in a review of 17 trials [11] and by about 18 mg/dL in a review of 50 trials [12]. Total cholesterol and triglycerides also fell in both [11][12]. The HDL ('good') cholesterol results disagree: one review found no change [11], a 2024 review of 34 studies found a rise [13], and a trial in type 2 diabetes found no change [14].

Blood pressure. Eleven trials with 860 people found systolic blood pressure about 3 mmHg lower than control, and diastolic about 3 mmHg lower [4]. A 2023 update found a similar drop of about 3 mmHg in both [15]. A 2026 review of 31 trials found systolic about 3 mmHg lower [8]. Single trials were mixed: in 55 adults with high blood pressure, black seed oil lowered systolic pressure more than placebo [16], while in 76 older adults it did not beat placebo [17].

Doses used in studies

Doses ranged from 200 to 4,600 mg a day across trials in a 2025 review [18]. Examples: 2 g of Nigella sativa a day for a year [5]; 2 g of oil a day for eight weeks [19]; 1,350 mg a day of oil capsules for three months [10]; 2.5 mL of oil twice a day for eight weeks [16]. These are study doses, not recommendations.

Safety and interactions

Side effects. In one trial of older adults, 6 of 38 people in the black seed group (15.8%) had indigestion, and some had nausea (7.9%) or constipation (5.3%) [17]. Other trials reported no serious side effects [1][3]. In a 90-day trial in healthy adults, 200 mg a day of a thymoquinone-rich oil caused no serious side effects and no change in liver or kidney tests [1]. For fatty liver disease, liver enzymes fell more than placebo and no adverse effects were reported [2].

Medicine interactions. No human trial testing interactions with blood thinners, diabetes or blood pressure medicines was found. One 12-month trial gave black seed alongside usual diabetes drugs; its abstract does not mention side effects [5].

Upper limits. No upper safe limit or toxic dose was found in the human trials read for this page.

Pregnancy and breastfeeding. No human studies were found. People who are pregnant or breastfeeding should ask a doctor first.

Kidney and bleeding disorders. No data were found for people with kidney disease or bleeding disorders.

Caveats and open questions

Most trials are small and short; the blood pressure trials averaged about eight weeks [4]. Forms differ: powder and oil gave different results for blood pressure [4] and for blood sugar [9]. Blood pressure reviews show very high variation between trials [15]. The safety trial tested a branded oil (BlaQmax), so its results apply to that product [1]. A phase 2 trial of black seed oil in type 2 diabetes (50 planned) is registered with status unknown [NCT03959306].