Who Should Not Take Oil of Oregano? Safety, Interactions and Side Effects

By Bill, founder of Wellora · Updated October 11, 2026

Oil of oregano is widely sold and generally well tolerated, but it isn't right for everyone. This page collects the main reasons to skip it, or to check with a doctor first, with a source for each. Our softgels also contain black seed oil, so it covers that too.

Quick list: talk to a doctor or skip it if you…

• are pregnant, could become pregnant, or are breastfeeding
• are buying for a child (our softgels are for adults 18+)
• are allergic to plants in the mint family, such as basil, lavender, marjoram, mint, sage or thyme
• take blood thinners or have a bleeding disorder, or have surgery coming up
• take diabetes medication, blood pressure medication, lithium, diuretics, or medicines that affect the immune system
• take medicines processed by the liver enzymes CYP2D6 or CYP3A4 (your pharmacist can tell you)

Pregnancy and trying to conceive

The NIH's LiverTox database says oregano in supplement doses should not be used during pregnancy, and advises against it for women who could become pregnant and aren't using contraception (LiverTox, NIH). WebMD also advises avoiding medicinal amounts in pregnancy (WebMD). The evidence behind this is limited, but every source we found agrees: avoid it.

Black seed oil is also considered likely unsafe in more than food amounts during pregnancy (WebMD; Cleveland Clinic).

Breastfeeding

There's no data on oregano supplements while breastfeeding. The NIH's LactMed database says amounts above what's normally found in food should probably be avoided (LactMed, NIH). There's also no data on whether black seed oil passes into breast milk (Drugs.com).

Children

Medical News Today advises against using oregano oil on children or infants (Medical News Today), and there's no established dosing for children. Our softgels are made for adults 18 and over. For a child, ask your pediatrician.

Allergies to mint-family plants

Oregano belongs to the mint family (Lamiaceae). If you're allergic to basil, lavender, hyssop, marjoram, mint, sage or thyme, you may also react to oregano (WebMD). Rash, and rarely a severe allergic reaction, has been reported after taking oregano (Drugs.com).

Blood thinners, bleeding disorders and surgery

Oregano may slow blood clotting, so WebMD advises caution with blood thinners and stopping about two weeks before surgery (WebMD). This is a theoretical concern; Drugs.com lists no well-documented interactions (Drugs.com). Black seed oil carries similar cautions around blood thinners and surgery (Cleveland Clinic), and sources disagree on how it interacts with warfarin (WebMD; Memorial Sloan Kettering). If you take any blood thinner, check with your doctor first.

Other medications

• Diabetes medication: oregano and black seed may both affect blood sugar, so the combination could add to your medication's effect (WebMD, oregano; WebMD, black seed).
• Blood pressure medication: black seed may lower blood pressure (WebMD).
• Lithium and diuretics: flagged as cautions for oregano (Medical News Today).
• Medicines processed by CYP2D6 or CYP3A4: black seed inhibits these liver enzymes in studies, and Memorial Sloan Kettering lists this under who shouldn't take it (MSK). Many common drugs use these enzymes.
• Immunosuppressants, sedatives and some other drugs: WebMD lists possible interactions with black seed (WebMD).
• Iron: oregano may reduce absorption of iron and other minerals (WebMD). If you take iron, ask about spacing them apart.

If you take any prescription medicine, show the label to your pharmacist. It takes them a minute.

Common side effects

Oregano is usually well tolerated. At higher doses it can cause stomach discomfort, heartburn, nausea, diarrhea or constipation, dizziness and headache (LiverTox, NIH). Black seed oil can cause stomach upset, bloating, an altered sense of taste, diarrhea and headache, and rarely a rash (LiverTox, NIH). Taking softgels with a meal, as our directions suggest, may help with stomach upset and burping.

Is it safe to take every day?

There isn't good long-term data in people. The clinical studies that exist are small and short, a few weeks to two months. Follow the label, don't take more than the serving size, and if you plan to take it for a long time, mention it to your doctor.

What the evidence does and doesn't show

Oregano isn't approved as a treatment for any disease. Its antimicrobial and other effects have been shown in lab and animal studies but not demonstrated in humans (LiverTox, NIH). For black seed, Cleveland Clinic says there's no robust evidence for any condition (Cleveland Clinic). We'd rather you know that up front.

If none of the above applies to you, our oil of oregano softgels list exactly what's in each serving. Here's how to read the label, and why you shouldn't swallow oregano essential oil.

These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. This article is for general information and isn't medical advice. Talk to your doctor or pharmacist before starting a supplement, especially if you're pregnant, breastfeeding, take medication, or have a health condition.