What it's called: Estrostep Fe, LoEstrin 1/20, Ortho-Novum 7/7/7, Ortho Tri-Cyclen Lo, Yasmin, Yaz.
What it does: This birth control mainstay is still 99% effective against pregnancy when taken around the same time every day. It's also known for easing hot flashes and restoring regular periods.
Who should avoid it: Smokers and those 35 or older. The estrogen may cause dangerous blood clots. If you suffer from migraines, you should also pass because it may trigger the painful headaches.
What it's called: Micronor, Nora-BE, Nor-QD, Ovrette.
What it does: Known as the mini pill, progestin-only meds don't contain estrogen. They're safer for smokers, diabetics, and heart disease patients, as well as those at risk for blood clots. They also won't reduce the milk supply for women who are breast-feeding.
Who should avoid it: If you have trouble remembering to take your pill at the same time every day, progestin-only pills might not be your best bet. They need to be taken at exactly the same time every day; if you're more than three hours late, plan on using a backup method.
What it's called: Lybrel, Seasonale, Seasonique.
What it does: These pills prevent pregnancy and allow you to have a period only every three months. (Note: Lybrel stops your period for a year, but you must take a pill every day, year-round.)
Who should avoid it: There's no evidence proving it's dangerous not to have periods, but there is still no long-term research to show that it is safe.
What it's called: NuvaRing.
What it does: The ring is made of flexible plastic and delivers estrogen and progestin, just like the combination pill. You place the ring in your vagina for three weeks, and then remove it for one week so that you have a regular period.
Who should avoid it: Women who smoke, or have blood clots or certain cancers, should not use the NuvaRing.
What it's called: Milex Wide Seal, Ortho All-Flex, Semina, SILCS.
What it does: Made of rubber and shaped like a dome, a diaphragm prevents sperm from fertilizing an egg. It covers the cervix and must always be used with a spermicide. Women must be fitted for a diaphragm in their doctor's office.
Who should avoid it: If your weight tends to fluctuate by more than 10 pounds at a time, the diaphragm may not work. If you gain or lose weight, you'll need to be refitted. Prone to bladder infections? You might want to consider another option. If you've had toxic shock syndrome, you shouldn't use a diaphragm.
What it's called: Mirena, ParaGard.
What it does: ParaGard is a surgically implanted copper device that prevents sperm from reaching the egg. Mirena, also surgically implanted, works by releasing hormones. Intrauterine devices (IUDs) are more than 99% effective and good for 10 years.
Who should avoid it: Some doctors recommend the device only for women who have given birth. When the device is implanted, your uterus is expanded, and this might cause pain in women who have not had children. If you're planning on having children in a year or two, look at other options. The IUD can be removed, but the high cost—up to $500—might not be worth it for short-term use.
What it's called: Femy, Protectiv, Reality.
What it does: The female condom is made of polyurethane, or soft plastic, and protects against STDs. It is inserted deep into the vagina, over the cervix, much like a diaphragm. Unlike the male condom, the female condom can be put into place up to eight hours before sex.
Who should avoid it: Male condoms offer more protection—both against STDs and pregnancy—than female condoms, so if you and your male partner aren't in a long-term, monogamous relationship, female condoms are not a perfect substitute.
What it's called: Durex, LifeStyles, Trojan.
What it does: Male condoms protect against pregnancy and STDs, including HIV. Worn properly, condoms prevent sperm from entering the uterus. Go with latex or polyurethane condoms; lambskins do not shield you against all STDs.
Who should avoid it: If your mate is allergic to latex or polyurethane, you'll have to find another option. And if you tend to use a lubricant that contains oil, such as hand lotion or baby oil, you'll need to switch to an oil-free option like K-Y Jelly, which, unlike oil-based lubricants, doesn't degrade latex.
What it's called: Ortho Evra.
What it does: You can place the hormone-releasing patch on your arm, buttock, or abdomen, and rest easy for one week.
Who should avoid it: If you're particularly at risk for blood clots, you might want to find a different method. The patch delivers 60% more estrogen than a low-dose pill, so you're at an increased risk for dangerous blood clots.
What it's called: Implanon, Norplant.
What it does: About the size of a matchstick, the implant is placed under the skin on your upper arm. Implants last for three years and can cost up to $800. They are nearly 100% effective.
Who should avoid it: Implanon may not work as well for women taking St. John's wort, or women who are overweight.
What it's called: Essure, tubal ligation, vasectomy.
What it does: Women can undergo either tubal ligation, a surgical procedure that blocks the fallopian tubes from carrying eggs to the uterus, or tubal implants (Essure), a nonsurgical technique in which a small coil is inserted into the fallopian tubes. The sterilization process is less risky for men: A vasectomy is a minor surgery in which the tubes that carry sperm from the testicles are cut.
Who should avoid it: If you plan to have children, sterilization is not an option—it's not designed to be reversible.
What it's called: Copper T IUD, Next Choice, Plan B, Plan B One-Step.
What it does: Emergency contraception is a backup for regular birth control. Plan B contains a higher dose of the same synthetic hormones found in the combination pill. It works best if taken within 72 hours of unprotected sex, but may work up to five days later. There's also the copper T IUD, which a doctor can insert into your uterus five to seven days after unprotected sex.
Who should avoid it: Plan B, known as the morning-after pill, is available over-the-counter at most pharmacies, but only to women 18 years and older. Minors need a prescription. Copper T IUDs can be very expensive—up to $500. Plus, they last for up to 10 years, so if you hope to get pregnant in the future, this isn't for you.