Is there a scientific/chemical explanation as to why Saint John's Wort is said t!

Is there a scientific/chemical explanation as to why Saint John's Wort is said to interfere with birth control

I know that there is anecdotal evidence that SJW can decrease the effectiveness of oral contraceptives, but is there any solid evidence or proof that it is actually the culprit in these incidences rather than there being another possible cause? If so, what is the chemical action that causes the interference? Also, is anyone aware of how greatly the oral contraceptive effect is decreased? Please HELP, because I want to try taking SJW as I can't afford anymore prescription antidepressants, but I can also not afford to get pregnant. Do I really need to worry or is the connection unproven? Thank you...

St. John's wort may alter the blood levels of drugs that are broken down by certain liver enzymes. This affects many different drugs, with potentially serious effects. If you are considering taking St. Johns wort with other drugs, herbs, supplements or vitamins, it is important for you to speak with your health care provider and pharmacist first.

The U.S. Food and Drug Administration suggests that you avoid St. John's wort if you are taking HIV and AIDS drugs called protease inhibitors, such as indinavir (Crixivan), or non-nucleoside reverse transcriptase inhibitors, such as nevirapine (Viramune). There is a risk of lowering the levels of these drugs in your body if you take them with St. John's wort. St. John's wort may also decrease the effects of tricyclic antidepressants, such as amitriptyline (Elavil); cholesterol-lowering drugs, such as lovastatin (Mevacor); nifedipine (Procardia); midazolam (Versed); digoxin; and theophylline. Avoid St. John's wort if you are taking an immunosuppressant drug such as cyclosporine, tacrolimus, or myophenic acid, especially if you have received an organ transplant; there have been multiple reports of significant reductions in drug levels and possible organ rejection.

St. John's wort may increase the risk of sun sensitivity when used with drugs such as tetracycline or tretinoin (Retin-A). St. John's wort may decrease the effects of the blood-thinning drug warfarin. Be careful if you take monoamine oxidase inhibitors, such as phenelzine (Nardil), or selective serotonin reuptake inhibitors, such as fluoxetine (Prozac), because of the potential for increased side effects when taken with St. John's wort.

Use St. John's wort cautiously if you are taking birth control pills, because of reports of altered menstrual flow, bleeding and unwanted pregnancies. St. John's wort may reduce the thyroid activity of drugs such as levothyroxine (Synthroid). St. John's wort may increase the anti-inflammatory effects of cyclooxygenase (COX-2) inhibitors, such as celecoxib (Celebrex), or nonsteroidal anti-inflammatory drugs, such as ibuprofen (Motrin).

St. John's wort may increase imatinib clearance. Thus, patients taking imatinib should avoid taking St. John's wort. Concomitant use of enzyme inducers, including St. John's wort, may necessitate an increase in the imatinib dose to maintain effectiveness.
St. John's wort has been shown to decrease the blood concentrations of omeprazole and affect the levels of tolbutamide, caffeine, dextromethorphan, fexofenadine, carbamazepine, and cimetidine, among other medications.

Interactions With Herbs And Dietary Supplements

St. John's wort may alter the levels of herbs or supplements that are broken down by certain liver enzymes. St. John's wort may add to the effects of other herbs and supplements that also affect the same liver enzymes, such as hops (Humulus lupulus). Iron absorption may be affected by St. John's wort.

Herbs with selective serotonin reuptake inhibitor or monoamine oxidase inhibitor activity may have increased levels if taken with St. John's wort. An example includes fenugreek. Levels of foxglove, oleander and cholesterol-lowering herbs may be reduced when these herbs are taken with St. John's wort. St. John's wort may increase sun sensitivity when used with other agents with similar effects, such as capsaicin. St. John's wort may decrease the thyroid activity of certain herbs.