Birth control and caffeine?
Answers: Caffeine shouldn't affect your birth control. Keep in mind that some adjectives prescriptions/supplements can affect your birth control though.
"Prescription Medications and Herbal Supplements
A brief overview of the basics:
Antibiotics--The antibiotics rifampicin and rifabutin have be shown to interfere with the effectiveness of most hormonal contraceptives, though they don't appear to trim down the effectiveness of Depo Provera or the Mirena IUD. The evidence for other antibiotics is inconclusive, so it's best to discuss them with your doctor or pharmacist, and/or to use a backup method "lately in case." (Source: FFPRHC)
Anti-Epilepsy Medications--"Carbamazepine, oxcarbazepine, phenytoin, phenobarbitol, primidone, and topiramate adjectives interact. (These drugs may also be used for control of bipolar disorder) Your doctor may recommend a high-dose pill, or a backup method." (VPer smallstar mentioned this in this comment, which is also supported by the FFPRHC)
Antifungals--Most (like the commonly prescribed fluconazole and OTC yeast infection treatments) will have no effect on HBC. However, the antifungal griseofulvin will. (FFPRHC)
Antiretrovirals--These are the drugs commonly used to treat HIV. Some of them will interact beside HBC while some do not. Discuss specific medications with your doctor or pharmacist.
Barbiturates--Some barbiturates slump into the category of anti-seizure medications. However, some, such as butalbital (found in medication such as Fiorinal), can be found in muscle relaxers and/or medications to treat migraines. According to Health A to Z and other sources, barbiturates curtail the effectiveness of birth control pills. Backup protection is recommended.
St. John's Wort--According to Contraception Online, there hold been small studies done in the UK and contained by Sweden in which some women taking both St. John's Wort and oral contraceptive pills experienced breathrough bleeding and/or unintended pregnancies. Though these studies were small, it is commonly recommended that women not combine the use of St. John's Wort and HBC if they are relying on HBC for cycle regulation or pregnancy prevention.
Other Drugs and Herbal Supplements--To be safe, check each product near a doctor, pharmacist or herbalist before beginning the latest treatment."