Black seed oil (Nigella sativa), also called black cumin or black caraway, is a herbal ingredient. Some studies suggest it may help with blood sugar, blood pressure, cholesterol, digestion, skin, and liver health.
The evidence for these benefits is limited. Black seed oil has been linked to several side effects, ranging from mild to severe.
Black seed oil can cause a rash, especially in people with allergies.
In a report from 2024, a person developed itchy red bumps, blisters, and swelling where the oil was applied, followed by severe skin peeling. Tests showed an allergy to black seed oil.
More case studies (reports on individual people) show reactions can range from mild rashes to severe allergies.
A 2024 study looked at black seed oil as a possible treatment for people with allergic rhinitis. Allergic rhinitis is when your nasal passages become inflamed as an immune response to allergens in the air like pollen, dust, or pet dander. This often makes the nose itchy, runny, or blocked.
People in the study reported side effects like dry nose, dry mouth, hoarseness, nausea, headaches, stomach upset, drowsiness, and tiredness.
Black seed oil can cause gastrointestinal symptoms such as:
- Nausea
- Vomiting
- Stomach pain
- Bloating
- Gastritis (irritated stomach lining)
- Abdominal cramps
- Indigestion (upset or uncomfortable stomach after eating)
- Constipation
Black seed oil has blood pressure-lowering effects. In some cases, this could cause blood pressure to become too low. A 2017 study showed black seed oil caused low blood pressure (hypotension) in some people with hypertension (high blood pressure).
A small 2013 study looked at the use of black seed oil in people with hepatitis C, a liver infection. Black seed oil caused hypoglycemia (low blood sugar), a potentially life-threatening condition, in some of the study participants.
In the same 2013 study on people with hepatitis C virus (HCV) infection, a 62-year-old person had kidney failure after using black seed oil for six days.
In a 2015 study, another person aged 51 developed kidney injury after taking high doses of black seed oil. The person had diabetes and high blood pressure.
In a 2024 case study, a 26-year-old person went to the emergency clinic with high liver and kidney tests, blurred vision, and loss of consciousness. The person had been taking 2,000 milligrams of black seed oil for a month.
Another 2024 case study reported that an 82-year-old person developed acute liver failure after using black seed oil. The person had extremely high liver enzyme levels and died on the ninth day of hospitalization.
Black seed oil can change how some medicines work. It affects certain enzymes in your body that break down drugs. If these enzymes are slowed down or sped up, the medicine can become stronger or weaker than it should be.
Black seed oil can interact with medications like:
- Blood thinners: Black seed oil can block the enzymes that break down blood-thinning drugs, such as Coumadin (warfarin). This may raise the risk of side effects such as nosebleeds, easy bruising, or internal bleeding.
- Blood pressure medications: Black seed oil may lower blood pressure. If you take it with blood pressure medications, your blood pressure could drop too low.
- Diabetes medications: Black seed oil can lower blood sugar. If you take it with blood pressure medications, your blood sugar could drop too low (hypoglycemia)
- Antidepressants: Black seed oil can increase serotonin levels. Some antidepressants also increase serotonin levels in the brain. This can cause higher serotonin levels than intended with the medication.
Always consult your doctor before taking herbal supplements. If you’re applying it to your skin, try a small patch first and wait a few days to check for any reaction.
