Originally published 2013-09-28.
Black seed, the small dark seed of the Nigella sativa plant, has a reputation that few kitchen spices can match. A well-known saying calls it a cure for every illness except death. The honest short answer is that black seed is a safe and flavourful spice in normal food amounts, and it is one of the most studied traditional remedies in the world, but there is still no strong clinical proof that it treats any disease on its own.
The research is real and often interesting. Much of it, however, comes from test tubes, animals or small human trials. Below you will find where the seed comes from, why it earned such a grand nickname, what the better studies have found, and who should be careful with it.
What black seed is
Nigella sativa is an annual flowering plant in the buttercup family, native to south-west Asia and the eastern Mediterranean. Its pale blue or white flowers turn into a seed capsule packed with tiny, angular, jet-black seeds. The genus name comes from the Latin niger, black, and sativa simply means cultivated.
Because the seed looks like several other spices, it has collected a confusing list of names. In English you may see it sold as black cumin, black caraway, nigella, fennel flower, Roman coriander or onion seed. In South Asian shops it is usually labelled kalonji, and in Russian cooking it is charnushka. It is not related to cumin, caraway, onion or sesame. To add to the muddle, the names "black caraway" and "black cumin" are also used for a different plant, Bunium persicum, so it is worth checking the Latin name on a supplement label.
In the kitchen the seed tastes slightly bitter, peppery and oniony. It is scattered over naan and Turkish breads, mixed into Bengali five-spice (panch phoron), and pressed into a dark, strong-smelling oil.
An old seed with an older reputation
People have grown this plant for a very long time. Seeds have turned up at a number of ancient Egyptian sites; the best known find comes from the tomb of Tutankhamun, who died around 1323 BC. A Hittite flask from the second millennium BC, found in Turkey, also held the seeds. Whether they were used as food, medicine or a burial offering is not always clear.
The seed travelled through Greek, Persian and Arab medicine. The Persian physician Avicenna (Ibn Sina) described it in his Canon of Medicine as a treatment for breathing difficulty. In Arabic it is often called habbat al-barakah, the "seed of blessing".
The famous phrase comes from Islamic tradition. A hadith recorded in Sahih al-Bukhari reports the Prophet Muhammad saying that black seed is a healing for every disease except death. For many believers this is a statement of faith and blessing rather than a medical instruction, and it explains why the seed is so widely used across the Muslim world today.
What is inside the seed
Roughly a third of the seed, about 32 to 40 percent, is oil. That oil is rich in linoleic acid, an omega-6 fat, along with oleic and palmitic acids. The seed also contains protein, small amounts of alkaloids and a group of aromatic compounds.
The compound researchers talk about most is thymoquinone. Alongside it are related molecules such as dihydrothymoquinone, p-cymene, carvacrol and thymol. In laboratory work, thymoquinone acts as an antioxidant and calms some inflammatory signals, which is why so many papers test it against so many conditions.
Lab studies have described a long list of possible actions for the seed and its extracts, including:
- anti-inflammatory and antioxidant effects
- antibacterial and antifungal activity
- lowering blood pressure and blood sugar in animals
- relaxing airway muscle (bronchodilator effect)
- protecting liver and kidney cells from toxins in animal models
A list like this sounds impressive, but it describes what a substance can do in a dish or a rodent. Plenty of compounds kill bacteria or cancer cells in a dish and then do nothing useful when a person swallows them, because the dose that reaches the tissue is far lower, or the body breaks the compound down first.
What human studies have found so far
Hundreds of papers now mention Nigella sativa. The human trials among them are usually small, short and run at a single centre, and many have not been repeated by independent teams. With that in mind, here is where the evidence stands for the uses people ask about most.
Blood sugar and type 2 diabetes
A 2010 Saudi trial in people with type 2 diabetes who were already on treatment reported that 2 grams of crushed seed a day, added for three months, lowered fasting glucose and HbA1c a little more than the comparison groups. Later pooled analyses point in the same direction. The changes are modest, and nobody has shown that the seed can replace diabetes medicine or regrow insulin-producing cells in people.
Blood pressure and cholesterol
A small 2008 Iranian study gave people with mild high blood pressure 100 or 200 mg of seed extract twice a day for eight weeks and found a fall in readings. A later meta-analysis judged the evidence for a short-term drop in blood pressure to be weak. A 2016 review suggested the seed may slightly lower total cholesterol, LDL and triglycerides.
Asthma and breathing
Some small trials, mostly from Iran, found that boiled seed extract eased asthma symptoms and improved lung tests. A double-blind trial in veterans injured by chemical weapons during the Iran-Iraq war reported fewer wheezing symptoms. These are encouraging signals, but they are not large enough to change how asthma is treated.
Infections
Seed extracts can stop the growth of bacteria, including some strains of MRSA, in laboratory dishes. A 2010 study in people with Helicobacter pylori found that the seed plus an acid-reducing drug cleared the infection in some patients, with results the authors compared to standard triple therapy. Claims that black seed "kills MRSA" in the body go far beyond this evidence.
Cancer
Thymoquinone slows the growth of colon and other cancer cells in the lab, and black seed oil reduced chemically induced colon tumours in rats. There are no good trials showing that black seed treats cancer in humans. Anyone with cancer should discuss any supplement with their oncology team, because some can interfere with treatment.
Other uses
Single small studies have looked at sore throat, children's seizures that did not respond to medicine, opioid withdrawal, eczema, acne and hair loss. Each is a lead for future research rather than a proven use.
Safety, side effects and interactions
As a cooking spice, black seed has an excellent record. The US Food and Drug Administration lists it as generally recognised as safe (GRAS) when used as a spice or flavouring. Concentrated capsules and oils are a different matter, because they deliver far more than a sprinkle on bread.
- Skin reactions: putting the oil directly on skin can cause allergic contact dermatitis, sometimes a severe, blistering rash.
- Stomach upset: some people report nausea, bloating or indigestion.
- Blood sugar and blood pressure: because the seed may nudge both downwards, it can add to the effect of medicines for diabetes or high blood pressure.
- Bleeding: it may slow blood clotting, which matters for people on blood thinners, with a bleeding disorder, or facing surgery.
- Kidneys: high doses over time have raised concern, and there is a case report of kidney failure in a person with diabetes who took large amounts.
- Pregnancy and breastfeeding: normal food use is considered fine, but supplements are not recommended.
If you are thinking of taking black seed as a supplement, especially alongside regular medicines, talk to a doctor or pharmacist first.
Common myths about black seed
"It cures everything except death." This is a religious and traditional saying, not a research finding. No food or plant has been shown to cure every disease.
"Hundreds of studies prove it works." The number of studies shows how much interest the seed attracts. Most are laboratory or animal work, and the human trials are mostly small. Quantity of papers is not the same as quality of proof.
"Natural means it cannot hurt you." Natural products can cause allergies, interact with medicines and harm the kidneys in high doses. The dose and the form matter.
"It can replace your medicine." Stopping prescribed treatment for diabetes, high blood pressure, asthma, infection or cancer in favour of black seed can be dangerous.
How to enjoy black seed sensibly
The easiest and safest way to get to know the seed is in food. Toast a teaspoon in a dry pan until fragrant and add it to flatbread dough, roasted vegetables, lentils, salads or yoghurt. A little goes a long way, because the flavour is strong.
If you buy oil or capsules, choose a product that names Nigella sativa on the label, store oil in a cool, dark place, and treat any health effect as a possible bonus rather than a promise. Black seed deserves its place in history and in the spice cupboard. It does not need to be a miracle to be worth knowing.
Sources: Nigella sativa (Wikipedia); WebMD: Are black seeds healthy?; Memorial Sloan Kettering, About Herbs: Nigella sativa; original article and study list: GreenMedInfo.
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