Does clary sage oil decrease the effectiveness of birth control pills?

Who knows?: There are not enough studies to show a benefit from this supplement and there are likely not enough to show definite interactions with bcp's. Ask your doctor, or just say no to herbal drugs that are not well studied. See http://www.rxlist.com/clary_sage/supplements.htm

Unknown: Keep in mind that natural products are not always necessarily safe and dosages can be important. Clary sage oil is safe when used in amounts found in foods. There isn't enough information to know if it is safe when used in medicinal amounts. The herb has been shown to increase the effects of choral hydrate causing excessive sleepiness and drowsiness. Its relationship to OCPs is unknown.