Black seed

What it is

Black seed comes from Nigella sativa, a flowering plant native to Eastern Europe and the Middle East that produces small black seeds. The seeds contain fixed oils such as linoleic, oleic and palmitic acid, plus volatile oils of which thymoquinone is the suspected main bioactive. The seed is used as a spice, and extracts are sold over the counter as liquids, powders and capsules. It has a long traditional-medicine history across a wide range of complaints.

What the research says

This is the best-studied of the three, and the picture is large reported effects sitting on weak foundations. An overview of 20 meta-analyses found benefit across many outcomes but rated 15 of those 20 reviews critically low quality, and graded 88 of 110 outcome indicators as very low certainty. A 2024 meta-analysis of 30 trials reports substantial falls in fasting glucose and HbA1c, but with heterogeneity above 92% and no effect on insulin or insulin resistance. Reported adverse events are mostly digestive, though a 2024 case report describes rhabdomyolysis, kidney injury and liver injury after black seed oil.

Evidence grade: Limited evidence.

What goes wrong

A 2024 case report in Toxicon describes acute kidney injury, rhabdomyolysis and hepatotoxicity following ingestion of black seed oil. (Source 1)

• Case report, Very low certainty.
• Size: 1 patient.
• Who: A person who had ingested black seed oil.
• How long: Acute presentation; the report does not state a duration of use in the abstract.
• Result: Three simultaneous injuries reported - muscle breakdown, acute renal damage and liver injury. A single case cannot establish causation or any rate, and the authors note that knowledge of black seed oil's adverse effects is currently limited.
• Funding: not stated.

Limit of this finding: A single case report. It gives no dose, no analysis of the product taken and no rechallenge, so it shows that this combination of injuries has been reported after black seed oil, not that black seed oil caused them, and it says nothing about how often this happens. It does, however, postdate the LiverTox assessment also cited in this entry, which was last updated in April 2023 and records no published reports of liver injury.

In this case report, we presented a case of acute kidney injury, rhabdomyolysis, and hepatotoxicity after ingestion of black seed oil.

Across the trials summarised in the umbrella review, the adverse events reported were mainly digestive, together with weakness and weight loss, and no study reported a serious adverse event. (Source 2)

• Review of reviews, Very low certainty.
• Size: 20 meta-analyses of randomised trials.
• Who: Adults across multiple conditions.
• How long: Varies by included review.
• Result: Stomach pain, diarrhoea, nausea, vomiting, weakness and weight loss; no serious adverse events reported in any included study. Trials were mostly short, so rare or delayed harms would not be captured.
• Funding: independent - National Natural Science Foundation of China.

Limit of this finding: 'No study has reported serious adverse events' records what short trials happened to report; it is not a demonstration of safety. The trials pooled here were mostly short and none was designed to detect rare or delayed harm. A case report published in Toxicon in 2024, also cited in this entry, describes rhabdomyolysis, acute kidney injury and hepatotoxicity after black seed oil, and it postdates and sits against this statement.

The main adverse events were digestive symptoms such as stomach pain, diarrhea, nausea, and vomiting, as well as weakness and weight loss. However, no study has reported serious adverse events.

What the evidence supports

A meta-analysis of 30 randomised trials found that Nigella sativa supplementation lowered fasting blood sugar and HbA1c, with very high statistical heterogeneity between trials. (Source 3)

• Meta-analysis, Low certainty.
• Size: 30 randomised controlled trials.
• Who: Adults; trials searched to December 2023.
• How long: Varied by trial; the review says longer durations are still needed.
• Result: Fasting blood sugar SMD -1.71 (95% CI -2.11, -1.31, p < 0.001; I2 = 92.7%); HbA1c SMD -2.16 (95% CI -3.04, -1.29, p < 0.001; I2 = 95.7%). Heterogeneity above 92% means the trials disagree with each other markedly, so the pooled figure should not be read as a reliable single effect.
• Funding: not stated.

Limit of this finding: The pooled numbers are almost certainly too large to be real. A standardised mean difference of -1.71 for fasting glucose and -2.16 for HbA1c is roughly two standard deviations, a bigger effect than metformin, and every outcome carries I2 above 92%, meaning the 30 trials disagree with one another so much that averaging them into a single number is not meaningful. Effects that large in a field of small trials usually reflect small-study and publication bias rather than a real benefit. The review also reports no results in ordinary units, so there is no way to tell what change in mmol/L, or in HbA1c percentage points, is being claimed. Read this as an unresolved signal, not as a measured benefit.

The pooled results using random effects model indicated that N. sativa supplementation significantly reduced FBS (SMD: −1.71; 95 % CI: −2.11, −1.31, p <0.001; I2 = 92.7 %, p-heterogeneity <0.001) and HA1c levels (SMD: −2.16; 95 % CI: -3.04, −1.29, p <0.001; I2 = 95.7 %, p-heterogeneity <0.001)

Position as of 27 April 2023: LiverTox (NIDDK) recorded no published reports of liver enzyme elevations or clinically apparent liver injury from black cumin seed products and assigned likelihood score E. A case report of hepatotoxicity was published in 2024, after that assessment. (Source 4)

• Official position, Certainty not rated.
• Size: Not applicable - a narrative safety assessment, not a study.
• Who: Users of black cumin seed products.
• How long: Assessment last updated 27 April 2023.
• Result: Likelihood score E, unlikely cause of clinically apparent liver injury, as assessed on 27 April 2023. A 2024 Toxicon case report of hepatotoxicity with rhabdomyolysis and acute kidney injury after black seed oil postdates this assessment and is recorded separately in this entry.
• Funding: government agency.

Limit of this finding: This is a position with a date on it. LiverTox was last updated on 27 April 2023, so 'no published reports' means none had been published by that date — it is not a statement about today. A case report in Toxicon in 2024, cited elsewhere in this entry, describes hepatotoxicity alongside rhabdomyolysis and acute kidney injury after black seed oil. Read the likelihood score E as the position as of April 2023, not as current reassurance, and read the two citations together rather than separately.

Despite widespread use, there have been no published reports of serum enzyme elevations or clinically apparent liver injury attributable to products containing black cumin seed.

What the evidence does not support

The same 30-trial meta-analysis found no effect of Nigella sativa on fasting insulin or on insulin resistance. (Source 3)

• Meta-analysis, Very low certainty.
• Size: Subset of the 30 randomised trials.
• Who: Adults.
• How long: Varied by trial.
• Result: Insulin SMD 0.48 (95% CI -0.53, 1.48, P = 0.353; I2 = 96.1%); HOMA-IR SMD -0.56 (95% CI -1.47, 0.35, p = 0.229; I2 = 95.0%). Both confidence intervals cross zero.
• Funding: not stated.

Limit of this finding: These two nulls come from the same pooling, with I2 of 96.1% and 95.0%, so the trials disagree with each other almost completely. That means the absence of an effect on insulin and insulin resistance is as uninterpretable as the large glucose effects reported in the same analysis, not a firm negative.

but not effect on insulin (SMD = 0.48; 95 % CI: −0.53, 1.48, P = 0.353; I2 = 96.1 %, p-heterogeneity <0.001), and HOMA-IR (SMD: −0.56; 95 % CI: −1.47, 0.35, p=0.229; I2 = 95.0 %, p-heterogeneity <0.001).

Across the umbrella review, Nigella sativa had no significant effect on the oral glucose tolerance test, fasting insulin, insulin resistance or postprandial blood glucose, and five studies found no change in HDL cholesterol. (Source 2)

• Review of reviews, Very low certainty.
• Size: Within 20 meta-analyses covering 187-3,679 subjects each.
• Who: Adults across multiple conditions.
• How long: Varies by included review.
• Result: Null for OGTT, fasting insulin, HOMA-IR and postprandial blood glucose; five of the included studies found no change in HDL-C.
• Funding: independent - National Natural Science Foundation of China.

Limit of this finding: These nulls carry the same quality problem as the benefits in the same review: 15 of the 20 pooled meta-analyses were rated critically low quality and 88 of 110 outcome indicators very low certainty, so this is weak evidence of no effect rather than evidence that there is none.

N. sativa had no significant effect on the oral glucose tolerance test (OGTT), fasting insulin levels, homeostasis model assessment of insulin resistance (HOMA-IR) and postprandial blood glucose (PPBG).

Where the evidence is mixed

An umbrella review of 20 meta-analyses concluded that Nigella sativa appears beneficial across various clinical outcomes, but rated the underlying reviews as mostly critically low quality and most outcomes as very low certainty. (Source 2)

• Review of reviews, Very low certainty.
• Size: 20 meta-analyses published 2013-2021.
• Who: Adults across multiple clinical conditions.
• How long: Varies by included review.
• Result: Methodological quality: 1 moderate, 4 low, 15 critically low. Of 110 outcome indicators, 5 moderate, 17 low and 88 very low certainty. The authors' own conclusion pairs the benefit claim with limitations in reporting and methodological quality.
• Funding: independent - supported by the National Natural Science Foundation of China (No. 82074420); authors declare no commercial or financial conflict.

Limit of this finding: The review's own conclusion that Nigella sativa 'is beneficial for various clinical outcomes' does not stand up against the figures printed beside it. Of the 20 meta-analyses it pooled, 15 were rated critically low methodological quality, and of 110 outcome indicators, 88 were graded very low certainty. Very low certainty means the real effect is likely to be substantially different from the estimate. The benefit sentence should never be read apart from those quality numbers.

This overview included 20 eligible meta-analyses published in peer-reviewed journals between 2013 and 2021. The overall methodological quality was relatively poor, with only one moderate quality, four low quality, and 15 critically low quality studies.

Where the research disagrees

Whether black seed products can injure the liver

• LiverTox, NIDDK, last updated 27 April 2023, position: In multiple, largely short term clinical studies of different preparations and concentrations of black cumin seed powdered extracts and oils, adverse side effects were usually described as uncommon and mild with either no change or slight improvement in serum aminotransferase and alkaline phosphatase levels. (Source 4)
• Toxicon case report, 2024, case-report: It is important to keep in mind that rhabdomyolysis, acute renal damage, and hepatotoxicity might occur following the use of black seed oil. (Source 1)

How much weight the reported benefits deserve

• The 2024 glycemic meta-analysis, meta-analysis: Overall, the evidence supports the consumption of N. sativa to reduce FBS and HA1c levels. (Source 3)
• The 2023 umbrella review of 20 meta-analyses, umbrella: Among the 110 outcome indicators of the quality of evidence, five were graded as moderate, 17 as low, and 88 as very low. (Source 2)

How much

• Reference intake: No reference intake (RDA or AI) exists for black seed. LiverTox describes it as an over-the-counter dietary supplement with a typical marketed dose of 300 to 1000 mg taken one to two times daily, which is a market convention rather than a reference intake set by any body. (Source 4)
• Upper limit: No upper limit or acceptable daily intake was found in the sources we could reach. LiverTox notes only that the FDA lists black cumin spice as generally recognized as safe, which is a food-additive status and not an upper limit. (Source 4)
• Studied: The trials pooled in the 2024 glycemic meta-analysis used a range of doses and durations that the authors say is still not settled - they state that more research is needed to determine the ideal dosage and duration. (Source 3)
• Studied: Marketed preparations described by LiverTox: liquid, powders and capsules, typically 300 to 1000 mg one to two times daily. (Source 4)

A common belief, and what the research shows

The belief: Black seed oil is a traditional food, so it cannot do real harm.

What the research shows: Most reported side effects are indeed mild and digestive - the umbrella review records "The main adverse events were digestive symptoms such as stomach pain, diarrhea, nausea, and vomiting, as well as weakness and weight loss. However, no study has reported serious adverse events." But a 2024 Toxicon case report describes something far more serious: "In this case report, we presented a case of acute kidney injury, rhabdomyolysis, and hepatotoxicity after ingestion of black seed oil." The authors add that "Although black seed oil is widely used around the world, there is currently limited knowledge on its adverse effects." Long use is not the same as systematic safety data.

Questions and answers

What is it?

Black seed is the seed of Nigella sativa, a flowering plant from Eastern Europe and the Middle East. The small black seeds are used whole as a spice and pressed or extracted for oil. Its chemistry is dominated by fixed oils and by volatile oils, of which thymoquinone is thought to be the main active compound. (Source 4)

What does it do in the body?

In pooled randomised trials the most consistent measured effect is on blood sugar markers: fasting glucose and HbA1c fall. The trials disagree with each other a great deal, and the same pooling found no effect on insulin or insulin resistance, so the mechanism behind the glucose change is not settled. (Source 3)

Is it good or bad for you?

Mostly benign in the short trials done so far, with digestive side effects the common complaint and benefits reported across many outcomes. The strong caveat is quality: the umbrella review that summarised the whole field judged the underlying meta-analyses poor and most outcome certainty very low, and a 2024 case report describes serious multi-organ injury after black seed oil. (Source 2)

How do you get more of it?

The seed is eaten as a spice, and extracts are sold over the counter as liquids, powders and capsules. LiverTox records the typical marketed dose as 300 to 1000 mg once or twice daily - a description of the market, not a recommendation. (Source 4)

If it is harmful, what reduces it?

Stopping intake is the only measure described. The reported harms are tied to ingestion of the oil, and no antidote or clearance procedure is described anywhere in the literature we searched; the Toxicon authors ask clinicians to consider black seed oil when these injuries appear. (Source 1)

Why might someone be low in it or missing it?

Does not apply in the nutritional sense. Black seed is a spice and supplement ingredient, not an essential nutrient, so there is no deficiency to be in. Someone has none simply if they do not eat the seed or take a product. (Source 4)

We searched: Searched for Nigella sativa or thymoquinone deficiency and essential-nutrient status via WebSearch; LiverTox and the 2023 umbrella review both describe it only as a traditional remedy and over-the-counter supplement, with no deficiency state.

Which whole foods contain it or feed it?

The whole food source is the seed itself, from the Nigella sativa plant, used as a culinary spice in Middle Eastern and South Asian cooking and known as kalonji or black cumin. Everything else - oils, powders, capsules - is processed from that seed. (Source 4)

What happens if you do not have it?

Nothing is described. There is no deficiency syndrome for black seed; the literature studies what adding it does, and even there the umbrella review grades most of the certainty as very low. Not taking it is the condition almost every control group in these trials was in. (Source 2)

We searched: Searched for Nigella sativa deficiency and black seed essential nutrient via WebSearch; the 2023 umbrella review of 20 meta-analyses reports only supplementation outcomes and no absence state.

How can you test for it?

No validated clinical test for black seed or thymoquinone status was found in the literature we searched. Trials measure downstream markers instead - fasting glucose, HbA1c, insulin and HOMA-IR - and none of these tells you how much black seed a person has taken. (Source 3)

We searched: Searched for thymoquinone plasma biomarker and Nigella sativa status test via WebSearch; the 2024 glycemic meta-analysis of 30 trials reports only glycemic outcome measures, and no status assay appears in the umbrella review.

References

1. Toxicon, volume 245, 107787. Rhabdomyolysis and acute kidney injury after consumption of black seed oil. 2024. DOI 10.1016/j.toxicon.2024.107787. Read the source
2. Frontiers in Nutrition. Nigella sativa and health outcomes: An overview of systematic reviews and meta-analyses. 2023. PMID 37057067, DOI 10.3389/fnut.2023.1107750. Read the source
3. Prostaglandins & Other Lipid Mediators. The effect of Nigella sativa supplementation on glycemic status in adults: An updated systematic review and meta-analysis of randomized controlled trials. 2024. DOI 10.1016/j.prostaglandins.2024.106885. Read the source
4. National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), NCBI Bookshelf. Black Cumin Seed — LiverTox: Clinical and Research Information on Drug-Induced Liver Injury. 2023. Read the source