Interactions Highlight: Natural Medicines & Oral Hormonal Contraceptives

General awareness about potential drug interactions with dietary supplements is on the rise. But it’s important to continue reiterating this with patients to help them understand why disclosing supplement use is so crucial. Both the effects and side effects of certain drugs can be altered when taken with some supplements. Let’s review a few notable interactions with oral hormonal contraceptives

Talk to patients about St. John’s wort. St. John’s wort interacts with a long list of drugs – it’s a strong inducer of cytochrome P450 3A4 (CYP3A4) enzymes and is also believed to induce 1A2 (CYP1A2) and 2C9 (CYP2C9), all of which are responsible for the metabolism of progestins and estrogens in contraceptives. It increases the clearance of these contraceptives and reduces their clinical effects, which has led to unplanned pregnancy. If patients are using St. John’s wort, make sure they understand that an alternative form of birth control is needed.

Also watch out for activated charcoal – it’s increasingly promoted for gastrointestinal issues including gas and bloating. It adsorbs various oral drugs and may reduce their absorption and/or half-life. There’s concern that it might reduce the absorption of oral contraceptives, thus reducing their effectiveness. But some clinical research shows that this risk is low when activated charcoal is taken at least 12 hours before or 3 hours after contraceptives. Advise caution.

There are several other moderate interactions to keep an eye on, including melatonin and fish oil. There’s some evidence that the effects of the natural medicines might be altered by the contraceptives – for example, taking contraceptives with melatonin might increase the effects and side effects of melatonin. Similarly, taking fish oil with contraceptive drugs might decrease the triglyceride-lowering effects of fish oil.

We’ll keep you up to date as new and notable interactions arise – we’re constantly adding new interactions to our monographs as they are identified. In the meantime, make sure to take advantage of our Interaction Checker.