A complete safety, timing, and dosage guide for combining Vitamin B3 (Niacin, Niacinamide) with St. John's Wort — including how the two supplements interact, the best time of day to take each, and which populations should be careful.
Yes, you can take vitamin B3 (niacin/niacinamide) and St. John's Wort together — no known interaction.
Vitamin B3 and St. John's Wort together are safe for most people. No significant interaction has been found, so you can combine them without worrying about reduced effectiveness or increased side effects.
St. John's Wort is a potent inducer of cytochrome P450 enzymes like CYP3A4 and CYP2C19, which can speed up the breakdown of many drugs. Niacin and niacinamide, however, are not significantly metabolized by these enzymes; instead, they are converted into NAD and NADP through a series of cellular enzymes. This means St. John's Wort does not accelerate the clearance of vitamin B3. It also does not alter niacin absorption or distribution. As a result, the two do not affect each other's activity in the body, though high-dose niacin can independently cause liver enzyme changes that are unrelated to St. John's Wort.
You can take both supplements together in the morning with breakfast to keep things simple. If you are using niacin for cholesterol-lowering (typically 500–2,000 mg daily), do this only under medical supervision and ask your doctor to check liver enzymes regularly. Take St. John's Wort at the same time each day to maintain steady blood levels. If you miss a dose of either supplement, skip it and resume your regular schedule—do not double up. Drink plenty of water with niacin to reduce flush symptoms.
Niacinamide is less likely to cause flushing than nicotinic acid (niacin), so it may be more comfortable if you are combining it with St. John's Wort. St. John's Wort potency varies by formulation, but this does not change its lack of interaction with either form of vitamin B3. Choose the B3 form that best fits your needs and tolerance.
Yes, you can take them together. They use separate metabolic pathways, so St. John's Wort doesn't speed up the breakdown of vitamin B3, and niacin doesn't alter St. John's Wort's active compounds. Taking them together with food is fine.
Yes, it is safe for most healthy adults to combine them daily at standard doses. Just stay within the tolerable upper limit of niacin (35 mg from supplements unless your doctor advises more), and remember that St. John's Wort can interact with other medications you take.
You don't need to wait at all—there is no established interaction, so you can take them at the same time. If niacin flushing bothers you, separating them by an hour or two may help, but it's not required.
No, they don't compete. Niacin is absorbed through sodium-dependent carrier transporters in the small intestine, while St. John's Wort's active compounds are relatively lipophilic and absorbed passively. These different absorption routes mean no interference.
People taking antidepressants, blood thinners, oral contraceptives, or immunosuppressants should avoid St. John's Wort entirely because it reduces drug levels. Those with liver disease should avoid high-dose niacin. Otherwise, the combination is safe at standard doses.
Take them with food to minimize stomach upset. Niacin can cause a flush, and food slows absorption, making the flush less intense. St. John's Wort is also well tolerated when taken with breakfast.
Reviewed by Caroline M. on April 8, 2026 for accuracy against the sources listed above. This page is educational and is not a substitute for professional medical advice.
The matrix has 86 supplements and 7310 pairwise interactions. Click any cell to see the full breakdown.