In general, when using birth control pills initially, the more common side effects are menstrual irregularities (bleeding or spotting), mood swings, bloating, headaches, acne, etc. It also slightly thickens the blood and increases risk of clogging blood vessels; this risk is significantly increased in smokers. This rarely happens but if it does, the consequences can be serious. Pills should be taken at the same time everyday; if perfect use is done, it is ~99.9% effective in preventing pregnancy. When taken everyday but not at the same time, the effectivity decreases to 95%. I do hope I have answered your question and take care always.
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