Alcohol would not decrease the effectiveness of the contraceptive pills, however it might cause you to get drunk more easily and have vomits, nausea and malaise with more ease as well.
On the other hand continuous alcohol intake while using birth control pills have been shown to increase the cholesterol levels in the blood.
These Q&A’s are for educational purposes and should not be relied upon as a substitute for medical advice you may receive from your physician. If you have a medical emergency, please call 911. These answers do not constitute or initiate a patient/doctor relationship.