Fact checked by Rebecca Thornton, M.S., Food Science and Human Nutrition
You picked up a bottle of black seed oil because you keep hearing good things about it. Then you searched for side effects and found warnings about kidneys, liver damage, and bleeding.
So which is it? Safe daily habit, or something to worry about?
Black seed has been tested in more than 80 human studies, and most people in them did fine. But there are a few real cautions, and they depend on how much you take, what else you take, and whether you put it on your skin. This guide walks through each one, with the actual numbers from the studies.
Quick answer: what are the side effects of black seed oil?
In human studies, the most common black seed oil side effects are mild and short-lived: stomach discomfort, bloating, a change in taste, loose stools, and headache [1]. The less common but more important cautions are:
- Skin reactions when used on the skin. Rashes, some of them severe, have been reported after putting the oil on skin [9, 10, 11, 12].
- Medication interactions. Black seed slowed how the body cleared a test medicine in a small human study [15]. It may also add to the effect of medicines that lower blood pressure or blood sugar [13, 14].
- Bleeding risk with blood thinners. This is mostly lab data plus one case report, but it is worth a conversation with your pharmacist [16, 17].
- Pregnancy and breastfeeding. Safety has not been studied, so it is best to skip it unless your provider says otherwise [18, 19].
What about your kidneys and liver? Pooled trial data do not show harm at typical doses [2, 5, 8], and the National Institutes of Health rates black cumin seed an unlikely cause of liver injury [1].
Is black seed oil safe to take every day?
For most healthy adults, daily use in amounts close to what studies tested appears to be well tolerated. Trials have lasted anywhere from 1 to 48 weeks [2].
Two trials in healthy adults are the most useful here, because they tested safety directly:
- 1 teaspoon a day for 8 weeks. Seventy healthy adults aged 34 to 63 took 2.5 mL of black seed oil twice a day (5 mL, about 1 teaspoon, in total) or a placebo. Liver and kidney blood markers did not change, and no side effects were reported [3].
- A small capsule dose for 90 days. Seventy healthy adults took 200 mg a day of a black cumin oil standardized to 5% thymoquinone. There were no serious side effects and no meaningful changes in liver or kidney markers [4].
What we don't know yet: how black seed oil affects people over many years, and how it behaves at doses above what trials have used. That is why the amount you take matters. See how much black seed oil the studies used below.
Can black seed oil hurt your kidneys?
At the amounts used in trials, the research does not show black seed oil harming the kidneys. On average, kidney markers stayed steady or moved in a healthy direction [2, 5]. There are two findings worth knowing about, though.
Where the kidney worry comes from
One case report. In 2013, doctors described a middle-aged man with other health conditions who developed sudden kidney injury after taking black seed [6]. A researcher who studies black seed replied in the same journal, arguing that black seed had not been shown to be the cause [7]. One case can't prove cause and effect, but it is the report most "kidney damage" warnings trace back to.
A higher-dose signal. A 2020 review pooled 19 trials with 1,295 people. Overall, black seed lowered blood urea nitrogen (BUN), a kidney marker. But in the 2 trials that used more than 2,000 mg a day, BUN went up. In 3 trials, creatinine, another kidney marker, rose by a very small amount [5].
What the bigger picture shows
The largest review so far pooled 82 studies with 5,026 people, at doses from 200 to 4,600 mg a day. Kidney markers such as creatinine and urea did not worsen on average [2]. The 8-week trial in healthy adults taking about 1 teaspoon a day also found no change in kidney markers [3].
Bottom line for your kidneys: stay near studied amounts. If you already have a kidney condition, take medicine that affects the kidneys, or get regular kidney blood tests, talk with your provider first. Your own situation matters more than trial averages.
Is black seed oil bad for your liver?
No, not based on current evidence. LiverTox, the National Institutes of Health database on supplement and drug liver injury, rates black cumin seed "E," meaning an unlikely cause of liver injury. It notes no published cases of liver injury linked to black cumin products [1].
Trial data agree. In a review of 8 controlled trials, AST, a liver enzyme, dropped slightly with black seed, and ALT did not change significantly [8]. The larger 19-trial review found no liver harm, with small drops in ALP and, in longer trials, AST [5].
If you have a liver condition or take medicine that is hard on the liver, check with your provider anyway. That is good practice with any supplement.
Why does black seed oil upset my stomach?
Stomach upset is the most common complaint. People report stomach discomfort, bloating, loose stools, and a change in taste [1]. These effects are usually mild and fade [1].
A few simple habits help:
- Take it with or after food, not on an empty stomach.
- Start small, such as half a teaspoon, and build up over a week or two.
- Mix it in. Stir it into yogurt, honey, a smoothie, or salad dressing to soften the peppery bite.
Can black seed oil cause a skin rash?
Yes. This is the side effect people are least likely to expect. Putting black seed oil on skin has caused allergic contact dermatitis, an itchy, red rash, in several published reports [9, 10]. A 2024 case series described 8 people with severe skin reactions after applying the oil [11]. In one rare case, a person developed a serious whole-body reaction after using it on the skin [12]. The NIH's LactMed database also lists allergic contact dermatitis as a known risk [18].
If you use black seed oil on your skin, scalp, or beard, patch test first:
- Dab a small amount on the inside of your forearm.
- Cover it and wait 48 hours.
- If you see redness, itching, bumps, or blisters, don't use it on your skin.
Stop right away if a rash spreads, blisters, or comes with fever, and get medical care.
Planning to use it in your hair? Our guide on how to use black seed oil for hair walks through ways to apply it.
Who should talk to a doctor before taking black seed oil?
Black seed can nudge a few body systems that some medicines also target. If any row below fits you, bring the bottle to your pharmacist or provider before you start.
| If you... | Why it matters | How strong is the evidence? |
|---|---|---|
| Take blood pressure medicine | Black seed lowered blood pressure by about 3 points (mmHg) in pooled trials [13], and in healthy adults too [3]. Combined with medicine, that could add up. | Human trials, pooled |
| Take medicine that lowers blood sugar | Pooled trials found lower fasting blood sugar with black seed [14]. Your medicine dose may need watching. | Human trials, pooled |
| Take a blood thinner or antiplatelet medicine | In lab tests, thymoquinone slowed an enzyme the body uses to break down warfarin [16]. One case report described a large bruise under the skin in a man taking two antiplatelet medicines, whose platelet count was also low from other treatment. It cleared up after he stopped everything that could affect bleeding [17]. | Lab data and one case report |
| Take any daily prescription | In 4 healthy adults, black seed (2.5 g twice a day for 7 days) slowed two liver enzymes, CYP2D6 and CYP3A4, that process many medicines [15]. | Small human study |
| Are pregnant or trying to get pregnant | No human safety studies exist. In rats, a black seed extract prevented pregnancy [19]. | Animal data only |
| Are breastfeeding | There is no data on whether black seed passes into breast milk or how it affects babies [18]. | No data |
| Have surgery coming up | Because black seed may affect blood pressure, blood sugar, and possibly bleeding, tell your surgical team and ask when to stop. | Precaution |
| Have a kidney or liver condition | Your own condition and medicines matter more than the averages from trials. | Precaution |
How much black seed oil did the studies use?
This is the part most articles skip, and it is the most useful. "Safe in studies" only means safe at the amounts and time frames those studies tested.
| Study | Who | Daily amount | How long | What happened |
|---|---|---|---|---|
| Phase 1 safety trial [4] | 70 healthy adults | 200 mg of oil with 5% thymoquinone (about 10 mg thymoquinone) | 90 days | No serious side effects; liver and kidney markers steady |
| Healthy adult trial [3] | 70 adults, ages 34 to 63 | 5 mL of oil (about 1 teaspoon), split into 2 doses | 8 weeks | No side effects reported; liver and kidney markers steady; blood pressure dropped |
| Medicine processing study [15] | 4 healthy adults | 5 g of black seed, split into 2 doses | 7 days | Slowed the breakdown of a test medicine |
| 19-trial review [5] | 1,295 people | Varied; above 2,000 mg in 2 trials | Varied | Kidney marker BUN rose only in the higher-dose trials |
| 82-study review [2] | 5,026 people | 200 to 4,600 mg | 1 to 48 weeks | Liver and kidney markers did not worsen on average |
The spoon math
One teaspoon of oil is about 5 mL, or roughly 4.6 grams. That puts 1 teaspoon a day right at the top of the range used in trials [2, 3].
Thymoquinone content matters too. It is the compound most black seed research focuses on, and it varies a lot between bottles. One study of oils sold in Malaysia found thymoquinone ranging from 0.07% to 1.88%, a 27-fold difference [20]. An oil guaranteed at 2 to 4% thymoquinone gives you roughly 90 to 180 mg of thymoquinone per teaspoon. A stronger oil means you need less of it, not more. Learn more in our guide to what thymoquinone is and why it matters.
A practical approach: start with half a teaspoon a day with food, work up to about 1 teaspoon, and talk with your provider before going beyond that, especially if you take any medicine.
How strong is the safety research? An evidence check
Not all evidence is equal. Here is how each concern stacks up.
| Concern | Best evidence in people | What it shows |
|---|---|---|
| Liver | NIH LiverTox review plus pooled controlled trials [1, 5, 8] | No harm found; rated an unlikely cause of liver injury |
| Kidneys | Pooled trials plus one disputed case report [2, 5, 6, 7] | No harm at typical doses; watch doses above 2,000 mg a day |
| Stomach | Side effects reported in trials [1] | Common, mild, short-lived |
| Skin (applied) | Case reports and a case series [9, 10, 11, 12] | Uncommon, but can be severe |
| Blood pressure and blood sugar | Pooled controlled trials [13, 14] | Small drops; matters if you take medicine for either |
| Medicine processing | One 4-person human study plus lab work [15] | Early signal; ask your pharmacist |
| Bleeding | Lab study plus one case report with other risk factors [16, 17] | Possible, not proven in people |
| Pregnancy and breastfeeding | None; animal data only [18, 19] | Unknown, so avoid unless your provider approves |
5 mistakes that raise your risk of side effects
- Stacking thymoquinone. Taking a high-strength oil plus black seed capsules plus a blend that contains black seed can quietly double or triple your dose. Add up every source.
- Taking it on an empty stomach. This is the fastest route to stomach upset. Take it with or after a meal.
- Skipping the patch test. Some of the most severe reactions in the research came from putting the oil on skin [11, 12].
- Not telling your pharmacist. Your pharmacist can only check for interactions they know about. Add your supplements to your medicine list.
- Buying an oil with unknown strength. If a bottle doesn't state its thymoquinone content or share third-party testing, you can't know your dose. Our guide to how to spot fake supplements and read a COA shows what to look for.
Starting black seed oil? Try a 2-week check-in
A short, simple log helps you notice how your body responds, and gives your provider useful notes.
| When | Amount | What to jot down |
|---|---|---|
| Days 1 to 3 | Half a teaspoon with a meal | Stomach comfort, taste, bowel changes |
| Days 4 to 14 | Up to 1 teaspoon with a meal | Same as above, plus any skin changes |
| If you check blood pressure or blood sugar at home | Any amount | Your usual readings, same time each day. Share any big changes with your provider. |
Stop and call your provider if you notice a spreading rash, swelling, unusual bruising or bleeding, dark urine, much less urine than usual, or yellowing of the skin or eyes.
Key takeaways
- Most black seed oil side effects are mild stomach issues that fade, especially when you take it with food [1].
- Pooled trials do not show kidney or liver harm at typical doses [2, 5, 8], and the NIH rates liver injury as unlikely [1].
- Doses above 2,000 mg a day were linked to a rise in one kidney marker in 2 trials [5]. About 1 teaspoon a day is the top of the well-studied range [2, 3].
- Patch test before putting it on skin, scalp, or beard [11].
- Talk with your pharmacist if you take medicine for blood pressure, blood sugar, or blood clotting, or any daily prescription [13, 14, 15, 16].
- Skip it during pregnancy and breastfeeding unless your provider says otherwise [18, 19].
Frequently asked questions
Is black seed oil safe for your kidneys?
At the amounts used in studies, pooled trial data do not show kidney harm [2, 5]. One case report linked black seed to sudden kidney injury [6], and doses above 2,000 mg a day raised one kidney marker in 2 trials [5]. If you have a kidney condition, ask your provider first.
Can black seed oil damage your liver?
Current evidence says no. The NIH's LiverTox database rates black cumin seed an unlikely cause of liver injury and notes no published cases [1]. Controlled trials found liver enzymes stayed the same or dropped slightly [5, 8].
Are there black seed oil side effects for women?
Trials have not found side effects specific to women. The main concerns are pregnancy and breastfeeding, where safety has not been studied [18, 19]. If you are pregnant, trying to conceive, or nursing, check with your provider before using it.
Does black seed oil interact with medications?
It may. In a small study of healthy adults, black seed slowed two enzymes that process many common medicines [15]. It can also lower blood pressure and blood sugar a little [13, 14], which could add to the effect of medicines for either. Ask your pharmacist before combining it with any prescription.
How much black seed oil is too much?
Most trials used between 200 mg and about 4,600 mg a day [2]. One teaspoon of oil is about 4.6 grams, so 1 teaspoon a day sits at the top of that range [3]. Talk with your provider before taking more.
Can black seed oil cause a rash?
Yes, mainly when it is put on the skin. Allergic skin reactions, some severe, have been reported [9, 10, 11]. Always patch test on your forearm for 48 hours first.
Is it safe to take black seed oil with oil of oregano?
We could not find any published human studies that tested the two together, so the safety of the combination is unknown. If you want to use both, show both labels to your pharmacist, especially if you take any medicine.
Does black seed oil raise blood pressure?
No. Studies show the opposite. Pooled trials found a small drop of about 3 points (mmHg) [13], and healthy adults taking 1 teaspoon a day also saw lower readings [3]. If you already take blood pressure medicine, ask your provider before adding it.
How we make our black seed oil
Our Organic Black Cumin Seed Oil is cold-pressed and guaranteed to contain 2 to 4% thymoquinone. It is third-party lab tested, so you know the strength of what you are taking. One serving is 1 teaspoon (5 mL), and there are 50 servings in each 250 mL bottle.
That is stronger than any of the oils in the market study above [20], so a little goes a long way. If you are new to black seed oil, start with half a teaspoon with a meal and see how you feel.
Your next step
Before your next dose, take 2 minutes to do three things: check how much you are taking against the study table above, write down any medicines you take, and bring both to your pharmacist. It is a quick conversation that can save you a lot of guesswork.
Want to go deeper? Read why everyone is talking about black seed oil again, or explore the Nourishing Nutrients health blog.
Sources
- National Institute of Diabetes and Digestive and Kidney Diseases. (2023). Black cumin seed. In LiverTox: Clinical and Research Information on Drug-Induced Liver Injury. National Institutes of Health. PubMed
- Jafari, A., Mardani, H., Faghfouri, A. H., et al. (2025). Does Nigella sativa supplementation improve cardiovascular disease risk factors? A comprehensive GRADE-assessed systematic review and dose-response meta-analysis of 82 randomized controlled trials. Pharmacological Research, 219, 107882. PubMed
- Fallah Huseini, H., Amini, M., Mohtashami, R., et al. (2013). Blood pressure lowering effect of Nigella sativa L. seed oil in healthy volunteers: A randomized, double-blind, placebo-controlled clinical trial. Phytotherapy Research, 27(12), 1849-1853. PubMed
- Thomas, J. V., Mohan, M. E., Prabhakaran, P., et al. (2022). A phase I clinical trial to evaluate the safety of thymoquinone-rich black cumin oil (BlaQmax®) on healthy subjects: Randomized, double-blinded, placebo-controlled prospective study. Toxicology Reports, 9, 999-1007. PubMed
- Razmpoosh, E., Safi, S., Abdollahi, N., et al. (2020). The effect of Nigella sativa on the measures of liver and kidney parameters: A systematic review and meta-analysis of randomized-controlled trials. Pharmacological Research, 156, 104767. PubMed
- Arslan, E., Sayin, S., Demirbas, S., et al. (2013). A case study report of acute renal failure associated with Nigella sativa in a diabetic patient. Journal of Integrative Medicine, 11(1), 64-66. PubMed
- Bamosa, A. (2014). Nigella sativa is a safe herbal product. Journal of Integrative Medicine, 12(1), 66. PubMed
- Azizi, N., Amini, M. R., Djafarian, K., & Shab-Bidar, S. (2021). The effects of Nigella sativa supplementation on liver enzymes levels: A systematic review and meta-analysis of randomized controlled trials. Clinical Nutrition Research, 10(1), 72-82. PubMed
- Steinmann, A., Schätzle, M., Agathos, M., & Breit, R. (1997). Allergic contact dermatitis from black cumin (Nigella sativa) oil after topical use. Contact Dermatitis, 36(5), 268-269. PubMed
- Zedlitz, S., Kaufmann, R., & Boehncke, W.-H. (2002). Allergic contact dermatitis from black cumin (Nigella sativa) oil-containing ointment. Contact Dermatitis, 46(3), 188. PubMed
- Zhivov, E., Johnston, C., & Shangraw, S. (2024). Nigella sativa (black cumin) oil: A case report and analysis exploring severe cutaneous manifestations and implications for patient care. Journal of Clinical and Aesthetic Dermatology, 17(12), 42-44. PubMed
- Fargeas, M., Calugareanu, A., & Ben-Said, B. (2022). Drug reaction with eosinophilia and systemic symptoms (DRESS) syndrome after topical use of Nigella sativa (black cumin) oil. Contact Dermatitis, 87(2), 203-204. PubMed
- Kavyani, Z., Musazadeh, V., Safaei, E., et al. (2023). Antihypertensive effects of Nigella sativa supplementation: An updated systematic review and meta-analysis of randomized controlled trials. Phytotherapy Research, 37(8), 3224-3238. PubMed
- Hallajzadeh, J., Milajerdi, A., Mobini, M., et al. (2020). Effects of Nigella sativa on glycemic control, lipid profiles, and biomarkers of inflammatory and oxidative stress: A systematic review and meta-analysis of randomized controlled clinical trials. Phytotherapy Research, 34(10), 2586-2608. PubMed
- Al-Jenoobi, F. I., Al-Thukair, A. A., Abbas, F. A., et al. (2010). Effect of black seed on dextromethorphan O- and N-demethylation in human liver microsomes and healthy human subjects. Drug Metabolism Letters, 4(1), 51-55. PubMed
- Wang, Z., Wang, Z., Wang, X., et al. (2022). Potential food-drug interaction risk of thymoquinone with warfarin. Chemico-Biological Interactions, 365, 110070. PubMed
- Arab, A., Ramezaninejad, S., & Salehifar, E. (2026). Extensive subcutaneous hematoma in a patient receiving Nigella sativa oil, dual antiplatelet therapy, and oxaliplatin-based chemotherapy: A case report. Hospital Pharmacy. Advance online publication. PubMed
- National Institute of Child Health and Human Development. (2025). Black seed. In Drugs and Lactation Database (LactMed®). National Institutes of Health. PubMed
- Keshri, G., Singh, M. M., Lakshmi, V., & Kamboj, V. P. (1995). Post-coital contraceptive efficacy of the seeds of Nigella sativa in rats. Indian Journal of Physiology and Pharmacology, 39(1), 59-62. PubMed
- Alkhatib, H., Mawazi, S. M., Al-Mahmood, S. M. A., et al. (2020). Thymoquinone content in marketed black seed oil in Malaysia. Journal of Pharmacy and Bioallied Sciences, 12(3), 284-288. PubMed
These statements have not been evaluated by the Food and Drug Administration. This content is not intended to diagnose, treat, cure, or prevent any disease.
This article is for educational purposes only and is not a substitute for medical advice. Always talk with your healthcare provider before starting black seed oil or any supplement, especially if you are pregnant, breastfeeding, have a medical condition, have surgery planned, or take prescription medicine.
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