What every man should know about his girlfriend’s birth control

Whether you love condoms or hate them, you have to give them credit for being straightforward: Slip one on a penis before having sex, and you’ve got a pretty good chance of preventing pregnancy.

And yet, while they’re easy to use (put on, block sperm) and accessible (in every drugstore), they still aren’t 100% effective. According to the CDC, 18 in 100 women will become pregnant using only condoms.

This is why many women turn to less straightforward—but more effective—birth control methods. Like progestin pills. Or Depo-Provera shots. Or copper intrauterine devices.

If these terms sound like science fiction to you, you’re not alone. The nitty gritty of what female contraception is and how it works can be confusing to the women who put it in their bodies—so it makes sense that men would be a little fuzzy on the details.

Both people in a sexual relationship are responsible for preventing unwanted pregnancies, though, so to empower those readers who don’t happen to have vaginas—and help them be as supportive as possible to their female partner’s needs—we’ve compiled this quick guide. Now join us on a path to contraception enlightenment.

What are all the birth control options for women?

The most popular types of female birth control are oral contraceptives (“the pill”), intrauterine devices (IUDs), shots, and implants—so those are the ones we’ll cover.

Each method comes with its own set of pros and cons, and a woman will generally decide which is right for her with her doctor. Sometimes finding the right option can be a process of trial and error, based on how a particular method affects her body.

How do these methods work, exactly?

One word: Hormones! Bear with me as we get a little eggy and spermy.

There are two types of oral contraceptives, and both contain hormones: The “combination pill” contains the hormones estrogen and progestin, and the “minipill” contains only progestin. Women who take the combination pill need to remember to take it every day, and women on progestin-only pills need to take it at the same time every day.

Generally speaking, estrogen prevents the body from releasing an egg to be fertilized. But combined, estrogen and progestin do other cool things as well, like thicken the mucus inside a woman’s cervix (which makes it harder for sperm to enter)! And thin the lining of her uterus (which makes it harder for a fertilized egg to attach to it)!

For women who’d prefer not to take a daily pill, there’s the birth control shot. Formally known as Depo-Provera, the shot contains a hormone similar to progesterone and is injected once every three months.

If your partner is not planning to have a baby for several years, she may opt for a longterm option like an IUD or implant. IUDs are little T-shaped devices that are inserted into the uterus. They come in both hormonal and non-hormonal varieties—plastic IUDs release hormones, copper IUDs do not—and prevent pregnancy for three to 12 years, respectively. (How do the non-hormonal copper IUDs work? Basically, the copper causes a woman’s uterus and fallopian tubes to produce fluid that is toxic sperm. Pow!)

Finally, implants are matchstick-sized rods that are inserted into the upper arm. They release the hormone progestin and are effective for up to three years.

What happens if your girlfriend is on the pill and forgets to take her daily dose—or runs out?

It’s a fact of life for women on the pill that, every now and then, they will forget to take a dose or run out. I personally have trouble remembering to refill my prescription (despite CVS auto-calling me twice a day), and I inevitably end up in panic mode almost every single month.

If your partner forgot to take her combination pill in the morning and it’s now evening, she can simply take the missed pill—and if you want to have sex, no backup method is needed. However, if she’s on progestin-only pills, be sure to use a backup method like a condom or diaphragm, because with that pill, timing really matters.

If you don’t have condoms lying around, offer to go get some. Whatever you do, try not to get too annoyed that she forgot—simply figure out a solution together. Trust us, she’s already stressed by her mistake, and stress is the opposite of sexy time.

If your girlfriend is on the shot and forgot to get her last dose—i.e., it’s been more than 12 weeks since her last injection—make sure to use a backup method during sex. When the shot is not received on schedule, roughly 6 in 100 women will get pregnant.

What if you find out that your girlfriend forgot to take her birth control after you had sex?

If your partner realizes she forgot to take her birth control and you already had sex (again, mistakes happen), you have a few options for preventing pregnancy. If she’s on the combination pill and only forgot to take one pill, odds are she’s not pregnant—and she can just take the missed pill as soon as she remembers.

If she forgot to take a pill for more than two days, however, or she’s on progestin-only pills, there’s a chance she could be at risk for pregnancy. Bear in mind that when taken “perfectly,” both the combination and progestin-only pill are more than 99% effective at preventing pregnancy—but when taken “typically,” they’re only 91% effective.

If you’ve entered a situation where pregnancy can happen, you can turn to emergency contraception, also known as Levonorgestrel pills, but most commonly known as Plan B. Emergency contraception is now available over-the counter (although some states make it easier to obtain than others), and it can be used up to five days after unprotected sex. However, the sooner the better—it’s less effective on days four or five.

If you (and she) decide to get Plan B, offer to go with your partner to the pharmacy. No one likes to buy it alone, and some pharmacy workers have that judgy look. Be supportive, don’t play the blame game, and offer to split the cost, which is roughly between $35 and $65.

Also, the morning-after pill tends to cause side effects like nausea, headaches, and an overall “I feel like crap-ness,” so don’t just have her take it and peace out. Text her to see how she’s doing throughout the day. Remember, it’s both of your responsibilities, and however stressed you’re feeling, she’s probably feeling that times a hundred.

What if your girlfriend doesn’t want to take hormonal birth control any more?

For some women, pumping hormones into their body can cause negative side effects such as bleeding between periods, nausea, weight gain, breast tenderness, mood swings, and headaches. It can also cause more serious side effects—while rare, these can include blood clots, stroke, and depression.

If the side effects are bad enough, your partner may decide that she no longer wants to take hormonal birth control. If that’s the case, your job is to be supportive. We get it, unprotected sex is fun and one of the perks of birth control—but if your partner feels it’s upsetting her body more than it should, she should be able to ditch it worry-free.

At this point, she may choose to get a copper IUD—or she may want to start having protected sex with the use of condoms or a diaphragm. (For the uninitiated, a diaphragm is a shallow, dome-shaped silicone cup that can be inserted into the vagina up to 24 hours before having sex. It prevents sperm from entering the uterus, but works even better with spermicide. Note that diaphragms do require a prescription.)

What if your girlfriend is worried about the cost of her birth control?

Under the Affordable Care Act, insurance companies are required to cover prescription contraception at no cost. So if you’re girlfriend is still paying for birth control—and some women have indeed reported being charged, since some insurance companies have failed to comply—she shouldn’t be.

If your partner is still paying, offer to help her figure out what’s up with her insurance company. And if she’s currently uninsured, offer to help split the cost, which can range from $0 and $50 per month.

What if your girlfriend needs to see an OBGYN about her birth control?

Like the dentist, going to the OBGYN is the opposite of fun. You get poked and prodded and scraped and have to talk about “how many partners you’ve had.” I personally always feel better if my boyfriend goes with me because he distracts me in the car with funny stories and takes me for frozen yogurt or tacos afterward. Other women prefer to go it solo.

Your job is to ask. Offer to go to the doctor with her if you have the time—or if you can’t make it or she’d prefer to go by herself, text her while she’s there with a “good luck” or “let me know if you need anything” (if she’s the kind of woman who appreciates that sort of thing). The little stuff helps many of us feel like we’re not in it alone—and we shouldn’t be.

Taryn Hillin is Fusion’s love and sex writer, with a large focus on the science of relationships. She also loves dogs, Bourbon barrel-aged beers and popcorn — not necessarily in that order.