What are the side effects of taking birth control?

Most have none: Most women who take birth control pills have no side effects, but the most common side effect in the first 1-3 months is irregular, unpredictable bleeding that gets better over time. Other possible side effects include breast tenderness, nausea, mood changes, headaches. One serious potential risk, although rare, is an increased risk of blood clots in your legs or traveling to your lungs.