Black seed, also known as Nigella sativa or black cumin, has been used for thousands of years as both a food additive and herbal remedy across the Middle East, Far East, and Asia. These small, aromatic seeds have found their way into traditional medicine systems worldwide, and modern research is beginning to validate some of the health claims that practitioners have made for centuries.

The seeds possess a distinctive, slightly peppery flavour that makes them popular in cooking. You’ll find them scattered across naan bread, mixed into cheese, added to pickles, and used as a finishing spice on salads throughout South Asian and Middle Eastern cuisines. Beyond culinary uses, black seed oil has become increasingly popular as a dietary supplement.

But what does the scientific evidence actually say? This article examines the research behind black seed’s purported health benefits, its potential side effects, and the people who should avoid using it.

What is black seed?

Nigella sativa is an annual flowering plant belonging to the Ranunculaceae (buttercup) family. It grows naturally across Eastern Europe, the Middle East, and Western Asia, though it’s now cultivated in many other regions.

The plant stands roughly 20 to 30 centimetres tall, producing delicate pale blue or white flowers with five to ten petals. After flowering, it develops inflated seed capsules containing the small black seeds that give the plant its common name. These seeds measure approximately 1 to 5 millimetres in size and bear some resemblance to sesame seeds.

Active compounds

Black seeds contain dozens of bioactive compounds. The most studied is thymoquinone, which makes up roughly 30 to 48 percent of the volatile oil content. The seeds also contain alkaloids (nigellicine, nigellidine), saponins, flavonoids like quercetin, and various fatty acids including linoleic and oleic acid.

Thymoquinone has drawn the most research interest because early studies suggested anti-inflammatory and antioxidant effects.

What are the health benefits of black seeds?

1. May support COVID-19 recovery

During the COVID-19 pandemic, researchers investigated whether traditional remedies might offer any benefit to patients. One randomised controlled trial involving 173 young adults with mild COVID-19 found that those who received nigella seed oil supplementation (500 mg twice daily for 10 days) recovered more quickly than those receiving standard care alone.

The study, published in Phytotherapy Research, suggested that early supplementation might help with symptom resolution. However, the small sample size means these findings should be interpreted cautiously. Larger, more rigorous trials would be needed before drawing firm conclusions about black seed’s role in viral infections.

Source: Koshak AE, et al. (2021). Phytotherapy Research. PMC8364675

2. May benefit non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) affects an estimated 20 to 30 percent of people in Western countries, with rates climbing alongside obesity and type 2 diabetes. The condition occurs when fat accumulates in liver cells and can progress from simple fatty liver through to cirrhosis.

A systematic review and meta-analysis examining six randomised controlled trials (358 participants total) found that supplementation with nigella seeds or oil improved several liver health markers compared with placebo. These included alanine aminotransferase (ALT), aspartate aminotransferase (AST), fasting blood glucose, HDL cholesterol, and inflammatory markers.

While promising, the authors noted that larger studies are needed to confirm these findings and determine optimal dosing.

Source: Askari G, et al. (2021). Complementary Therapies in Medicine. PMID: 33728708

3. May help with asthma control

Asthma is a chronic inflammatory condition affecting roughly 10 percent of the population. Symptoms include wheezing, breathlessness, chest tightness, and coughing, which vary in frequency and severity.

A meta-analysis of four randomised controlled trials (187 participants with diagnosed asthma) found that supplementation with nigella extract or oil improved asthma control test scores and forced expiratory volume compared with control groups. The improvements appeared modest but consistent across studies.

That said, the research didn’t show significant effects on all respiratory markers, and the authors emphasised that more long-term studies are needed.

Source: Koshak A, et al. (2020). Journal of Asthma. PMID: 31892440

4. May improve male fertility

Male factors contribute to roughly 40 to 50 percent of all infertility cases, with many men showing abnormal sperm parameters such as low count, poor motility, or abnormal morphology.

A randomised, double-blind, placebo-controlled trial examined the effects of nigella seed oil (5 mL daily for two months) in 68 men with abnormal semen parameters. The results showed improvements across multiple measures including sperm count, motility, morphology, and semen volume.

The mechanism isn’t clear, though the antioxidant compounds in black seeds might protect sperm from oxidative damage. Worth mentioning to a doctor if you’re dealing with fertility issues.

Source: Kolahdooz M, et al. (2014). Avicenna Journal of Phytomedicine. PMID: 24680621

5. May reduce inflammation markers

C-reactive protein (CRP) is a blood marker that rises in response to inflammation throughout the body. Chronically elevated CRP has been associated with increased risk of cardiovascular disease and other health problems.

A systematic review and meta-analysis of five randomised controlled trials (439 participants) found that intake of nigella seeds or oil over 6 to 12 weeks significantly reduced serum CRP levels. Subgroup analysis revealed the effect was most pronounced in participants with obesity (BMI ≥ 30 kg/m²).

Lower inflammation might explain some of the other effects attributed to black seeds.

Source: Mousavi SM, et al. (2019). Complementary Therapies in Medicine. PMID: 31331553

6. May improve blood lipid profiles

Dyslipidaemia refers to abnormal levels of cholesterol and triglycerides in the blood. Having elevated LDL cholesterol, total cholesterol, or triglycerides whilst having low HDL cholesterol increases cardiovascular disease risk.

A large meta-analysis examining 17 randomised controlled trials (1,185 participants) found that nigella supplementation reduced total cholesterol by an average of 15.65 mg/dL, LDL cholesterol by 14.10 mg/dL, and triglycerides by 20.64 mg/dL. The analysis also noted that black seed oil appeared more effective for lowering harmful lipids, whilst black seed powder was better at raising beneficial HDL cholesterol.

Source: Sahebkar A, et al. (2016). Pharmacological Research. PMID: 26875640

7. May assist blood sugar control

Type 2 diabetes remains one of the most common chronic conditions worldwide, characterised by insulin resistance and impaired insulin secretion. Maintaining good glycaemic control helps prevent complications affecting the kidneys, eyes, and nerves.

A systematic review and meta-analysis of 17 randomised controlled trials found that oral nigella seed supplements reduced fasting blood glucose by approximately 17.84 mg/dL, post-meal blood glucose by 14.79 mg/dL, and glycated haemoglobin (HbA1c) by 0.57 percent compared with control groups.

Interestingly, subgroup analysis suggested that black seed oil performed better than black seed powder for improving fasting glucose levels.

Source: Daryabeygi-Khotbehsara R, et al. (2019). Journal of Ethnopharmacology. PMID: 30873688

8. May support weight loss

Obesity affects roughly 35 percent of adults in developed countries, with many people struggling to achieve and maintain a healthy weight despite repeated attempts.

A systematic review and meta-analysis of 13 randomised controlled trials (875 participants) found that supplementation with nigella seeds reduced body weight by an average of 1.76 kg and body mass index by 0.85 kg/m². Whilst modest, these effects were statistically significant. However, waist circumference didn’t show significant changes.

The proposed mechanisms include reduced fat absorption and effects on fat cell development, though these haven’t been confirmed in humans.

Source: Mousavi SM, et al. (2018). Journal of Functional Foods. PMID: 29559374

9. May help regulate blood pressure

Essential hypertension accounts for 90 to 95 percent of high blood pressure cases and represents a major risk factor for heart disease, stroke, and kidney failure. For every 20 mmHg increase in systolic blood pressure above 115 mmHg, the risk of fatal coronary events roughly doubles.

A systematic review and meta-analysis of 11 randomised controlled trials (860 participants) found that oral nigella seed extract reduced systolic blood pressure by an average of 3.26 mmHg and diastolic pressure by 2.80 mmHg compared with placebo. Interestingly, the powder form appeared more effective than oil.

Whilst these reductions are modest, they could contribute to overall cardiovascular risk reduction when combined with other lifestyle measures.

Source: Sahebkar A, et al. (2016). Pharmacological Research. PMID: 27512971

10. May help dissolve kidney stones

Kidney stones are crystalline deposits that form in the kidneys and can cause severe pain, blood in urine, urinary tract infections, and even hydronephrosis (kidney swelling due to urinary obstruction).

A randomised, triple-blind, placebo-controlled trial followed 60 patients with kidney stones larger than 5 mm over 10 weeks. The results were striking: in the nigella seed group, 44.4 percent of patients completely passed their stones, 51.8 percent saw their stones shrink, and only 3.7 percent showed no change.

Compare this with the placebo group, where just 15.3 percent achieved complete stone clearance, 11.5 percent saw reduction, 15.3 percent actually had stones grow larger, and 57.6 percent showed no change.

These findings suggest black seeds may help both prevent stone formation and assist in passing existing stones. For those prone to kidney stones, this could be worth exploring with a urologist.

Source: Ardakani Movaghati MR, et al. (2019). Phytotherapy Research. PMID: 30873671

Are there side effects of black seeds?

For most people, consuming black seeds in small amounts as a food ingredient is considered safe. When taken as supplements (oil or powder), short-term use in moderate doses hasn’t produced significant side effects in most studies.

However, reported adverse reactions include:

Stomach upset and nausea
Vomiting
Constipation
Abnormal liver enzyme values (ALT, AST, Gamma-GT, ALP), particularly at high doses

The safety of long-term supplementation hasn’t been established, so caution is warranted for extended use.

Safety precautions: 7 contraindications

Some people should be careful with black seed supplements:

Allergies - Some people develop skin rashes from black seeds, whether applied to skin or taken orally.
Pregnancy - Animal studies found black seed oil may slow uterine contractions. Check with your doctor first. (PMID: 8733115)
Breastfeeding - No safety data exists. Best to avoid or ask your doctor.
Bleeding problems or upcoming surgery - Black seed oil may thin the blood. Stop taking it at least two weeks before any surgery.
Diabetes medication - Since black seeds can lower blood sugar, they may strengthen your diabetes medication more than expected. Keep a close eye on your glucose levels.
Blood pressure medication - Same principle as diabetes meds. The combined effect could drop your blood pressure too low.
Other medications - Black seeds may interfere with how your liver processes drugs (specifically, they may inhibit cytochrome P450 enzymes). This could make some medications stronger or cause more side effects. Talk to your pharmacist if you take prescription medicines.

What to make of all this

Black seeds have been used in traditional medicine for centuries, and the research so far is cautiously encouraging. The blood sugar, cholesterol and inflammation studies are reasonably consistent, even if the effects are modest. The kidney stone trial stands out as particularly promising, though it’s just one study.

The honest assessment: most trials have been small and short. We don’t have good long-term safety data. If you’re thinking about trying black seed supplements, talk to your doctor first, especially if you take any medications.

For those interested in supporting urinary and kidney health naturally, you might also want to read about top health foods for optimal urinary health or learn more about conditions like kidney stones and urinary tract infections.

References

Koshak AE, et al. (2021). Nigella sativa supplementation to treat symptomatic mild COVID-19: A structured summary of a protocol for a randomised, controlled, clinical trial. Phytotherapy Research. PMC8364675
Askari G, et al. (2021). Effect of Nigella sativa supplementation on hepatic steatosis: A systematic review and meta-analysis. Complementary Therapies in Medicine. PMID: 33728708
Sahebkar A, et al. (2016). A systematic review and meta-analysis of randomized controlled trials investigating the effects of Nigella sativa oil on blood lipids. Pharmacological Research. PMID: 26875640