context: For many women, birth control pills are a good choice to prevent a pregnancy. It's easy to get a prescription from your doctor, and they're generally safe and effective. They're pretty hassle-free, too. You just have to remember to take a pill every day. Different types are available. If you're thinking about using one of them, here's what you should know to help you make a smart choice. Most women in the U. S. who are on the pill take what's called the combination pill. It uses man-made versions of the hormones estrogen and progesterone to keep you from getting pregnant. These hormones stop your ovaries from releasing eggs, and they also make changes in your cervix and uterus that lower your chance of a pregnancy. Another type is the mini-pill. It uses only man-made progesterone. It works mostly by causing changes that keep sperm from reaching eggs. You have less than a 1% chance of getting pregnant if you use them exactly as directed. That means taking your pill every day. Their effects are easy to reverse, too. When it's baby-making time, just stop taking them. It's possible to get pregnant right away. Usually, if you miss two of these pills in a row, you'll need to use backup birth control for a week. Combo pills have benefits beyond birth control. They help regulate your period and lessen cramping. They can lower your risk of certain cancers. They might clear your acne. Two brands, ( Beyaz, Yaz) are approved to treat a severe form of premenstrual syndrome. You might have: Changes in your period Headache and nausea Tender breasts Breakthrough bleeding (bleeding between periods, also known as spotting) More-serious but rarer side effects include: High blood pressure Heart attack or stroke Blood clots (the risk is highest for very overweight women) You shouldn't take a combination pill if you already have high blood pressure or have had a heart attack, stroke, or blood clots. Some pills ( Beyaz, Gianvi, Yasmin, Yaz, and others) use a man-made progesterone called drospirenone. These are linked to a higher risk of blood clots than brands that use other kinds of synthetic progesterone. These types of pills also aren't right for you if you have migraine headaches that affect vision, or if you gave birth less than 3 weeks ago. You're at greater risk of serious side effects if you smoke, especially if you're over 35. If you're not ready to quit, ask your doctor about other birth control options. Most of them use between 20-35 micrograms of estrogen, along with some man-made progesterone. Your doctor may start you on this level and then change it if side effects bother you. Some pills have as little as 10 micrograms of estrogen. Low-dose pills may be a good option if you're in perimenopause. They can help with symptoms like hot flashes or irregular periods. Combination pills are either monophasic (one phase) or multiphasic (multi-phase). Monophasic pills deliver an even level of hormones throughout the month. Multiphasic ones have slightly different levels of hormones in active pills. They mimic normal hormonal changes that happen during your menstrual cycle. Both are equally effective at preventing a pregnancy. It depends on the kind you choose. Monthly: Pills come in 21- or 28-day packs. With 21-day pills, you take one every day for 3 weeks straight. During week 4 you take no pills and have your period. The 28-day packs include pills with hormones and some inactive pills with none. With most brands, you take 21 active pills, and seven inactive ones to keep you in the habit of taking it every day. You'll have your period during the days you take the inactive pills. Other brands include 24 active pills and four that aren't. You may have shorter periods with this type. Extended-cycle: You take pills with hormones for 12 weeks straight and inactive ones for a week. You only have three or four periods a year. Continuous-use: You take an active pill every day and never have a period. You might have breakthrough bleeding, especially at first. You may want fewer periods or none at all, especially if you have problem periods. But you may wonder how you'll know if you get pregnant by accident. If you think you could be, take a pregnancy test. They work even if you're taking the pill. If the test is positive, stop taking your pills and call your doctor. It may be a good choice if you smoke or can't use the combination pill because of the estrogen. If you had estrogen-linked side effects, like tender breasts or nausea, even after switching to a low-dose pill, you may want to try the mini-pill. It's a safe choice if you have high blood pressure or other conditions that can be aggravated by estrogen. It's also an option if you just gave birth or are breastfeeding. It won't affect your milk supply or hurt your baby. Common side effects are similar to the combination pill, but bleeding can be more unpredictable. You may have spotting, heavy periods, or no period at all. It's as effective as the combination pill. But it's trickier to take. You must swallow it at the same time each day. If you're late by more than 3 hours, it becomes less effective. If this happens, you need to use backup birth control (such as condoms) for the next 2 days. All 28 mini-pills are active. They might not be the best option for you. So talk to your doctor before you choose your contraception method. Make sure she knows your health history and any other medications you take. Some meds make the pill less effective. This includes herbal remedies like St. John's wort. You shouldn't take any type of birth control pill if you've had breast cancer. Also, the pill doesn't protect you from STDs.