IMO, nothing kills a hookup mood quite like a birth control mishap. Seriously, I’ll take an awkward sex dream about my high-school math teacher any day over an unplanned pregnancy scare.

Of course, Americans now have affordable, over-the-counter access to emergency contraception pills in case of SOS situations like these. But that doesn’t necessarily make a birth-control fail any less stressful. As someone who’s personally had to take the “morning after” pill a few times in my life, in each instance I’ve worried about how it’s going to affect me. Will it actually work? What will that high dose of hormones do to my body in the long-run? (After all, hormones affect everything.) Since I know I’m not the only one who’s grappled with those questions, I asked a few doctors to address what a person might expect from their emergency contraception experience if it ever arises in their life.

First, a few caveats. No two people’s bodies are the same and everyone’s experience (especially side effects-wise) will be a bit different. Plus, it’s important to respect the “emergency” part of EC when you’re thinking about taking the morning after pill—it doesn’t prevent STIs and isn’t designed to be used on the reg, so most experts agree that it should never be considered your primary form of birth control.

However, it can definitely be a helpful ally in certain circumstances. So read on, whether you need the advice right now or not—because you can never be too prepared when a BC malfunction strikes.

When should a person take emergency contraception?

TL;DR: If you’re ever in a situation where you’re asking yourself if you should take emergency contraception…the answer is likely yes. “Any time that a woman thinks that recent sex may result in a pregnancy she doesn’t want is a good time for EC,” says Kate White, MD, MPH, who is an associate professor of OB/GYN at Boston University. “Certainly sex with no birth control in play is a good time [for emergency contraception], but so is sex where the condom breaks, or slips off your partner before he removes himself (and the condom) from you.” If your partner pulled out before ejaculating, he may still have released pre-ejaculatory fluid, and it’s unclear whether that substance contains sperm or not. So if you’re concerned about pregnancy in this situation, talk with your doctor to determine the best course of action for you.

If a person is on a reliable form of hormonal birth control—the pill, the patch, the ring, the shot—and using it properly, they likely wouldn’t need to take emergency contraception, says Pari Ghodsi, MD, FACOG, an obstetrician-gynecologist and spokesperson for Power to Decide. Emphasis on the “using it properly” part, since these forms of birth control can be less effective if not used as directed (like not taking the pill at the same time every day). Dr. White says that in general, a person should take emergency contraception if they were sexually active and missed more than two birth control pills this month, put their next patch on or ring in late, or were late for their next Depo-Provera injection.

What are the emergency contraception options?

The most well-known form of EC is Plan B One-Step, a single pill that contains a high dose of a synthetic progestin hormone called levonorgestrel. (There are also several other brands that include the same dose of levonorgestrel as Plan B, including Take Action, Next Choice, My Way, Aftera, and Preventeza.)

“Progestin is a hormone in birth control pills and other forms of hormonal birth control,” explains Dr. Ghodsi. “It stops or delays ovulation to prevent pregnancy, and it should be taken as soon as possible after having unprotected sex.” She adds that progestin-only EC is most effective when taken within three days of unprotected sex. Anyone at any age can purchase it over the counter without a prescription—some pharmacies keep it in the condom aisle, while others store it behind the checkout counter. You can also get it at health clinics like Planned Parenthood.  It costs around $35 to $60 out of pocket.

Another hormonal option is Ella, which is also known as ulipristal. Like progestin-only pills, it works to delay or stop ovulation. The difference is that it remains highly effective for up to five days after unprotected sex, compared to three to five days with progestin-based EC, and it’s only available with a prescription. “When taken as directed, ulipristal is more effective in preventing pregnancy than progestin-only [pills],” says Dr. Ghodsi. However, Ella is not recommended for people already on hormonal birth control, since it might render it less effective. It usually costs about $50, although can be a bit more if you order it online.

For a non-hormonal option, the copper IUD (intrauterine device) can actually work as an emergency contraceptive. In fact, says Dr. Ghodsi, this tiny T-shaped piece of copper-wrapped plastic is actually the most effective option—if it’s placed into the uterus within five days of having unprotected sex. “The copper IUD works mainly by making sperm less able to fertilize the egg,” Dr. Ghodsi explains. Adds Dr. White: “They can either stay in place for [up to 10 years] to provide ongoing birth control, or be removed after your next period, when you know you’re not pregnant.” The copper IUD may also be free, depending on one’s insurance plan, thanks to the Affordable Care Act. (If you’re curious about the IUD, here’s what real women have to say about theirs.)

How effective is emergency contraception?

When it comes to hormonal EC, effectiveness depends on a few factors, says Dr. White. In general, Plan B and other levonorgestrel-based pills are said to be 75-89 percent effective when taken within three days of having unprotected sex. (Although it does maintain some degree of efficacy for up to five days.) Ella is believed to lower your chances of getting pregnant by 85 percent if you take it within five days. (Oh, and hormonal EC does not work to induce abortion, contrary to what you may have heard.)

The tricky part: Hormonal EC prevents ovulation, so if you had unprotected sex in the 12 to 16 days before your next anticipated period (aka the time in your cycle when ovulation usually occurs), Plan B and other types of pills might not be effective. “You really only need EC before you ovulate—once the egg is out, there’s no stopping it,” says Dr. White. Some experts claim that the morning after pill can also stop a fertilized egg from implanting into the uterus, but Dr. White says there’s not enough scientific intel to back this up. “The studies of the efficacy of oral EC show that the effectiveness is essentially zero after ovulation, so that’s what I base my recommendation on. It’s a theoretical possibility that oral EC can prevent implantation, but it’s not born out by the data.”

The other issue is that hormonal EC may not be as effective for women who have a higher BMI. “For levonorgestrel EC (like Plan B), the pills are not likely effective if your BMI is over 26,” says Dr. White. “For ulipristal (Ella), the pills are not likely effective if your BMI is over 35. Hormone metabolism is different in women with higher BMIs, and that affects the levels of the medication in your blood, thereby reducing effectiveness.”

The copper IUD, on the other hand, is equally effective for women of all sizes (because there are no hormones to metabolize), and it may still work even if you have ovulated recently, since it affects sperm motility. But remember, time is of the essence, so see your doctor stat if this is the route you want to take.

Does EC come with any side effects?

Gnarly side effects thankfully are pretty rare. “About 20 percent of women may get headaches following EC treatment, 15 percent may have cramping, and about 10 percent will have nausea,” says Dr. White. “The other symptoms are less common than that.” (Other side effects include vomiting, dizziness, and breast tenderness.)

You may also find that your next period comes early, starts late, or is heavier or lighter than usual. This is normal, says Dr. Ghodsi, and it should resolve itself after just one cycle.

If you opt for the copper IUD, it’s worth noting that some women experience longer, heavier, more painful periods with this form of birth control. But again, it’s different for everyone.

How can a person tell if their emergency contraception worked?

Generally, getting a period after taking EC is a pretty good sign that you’re not pregnant. However, as mentioned before, the first period after taking EC might be later or lighter than usual. Making things even more confusing, there’s a period-like phenomenon called implantation bleeding that sometimes occurs in the very early stages of pregnancy—it resembles spotting or a light period, and it happens when a fertilized egg attaches to the uterine wall (usually within six to 12 days of conception).

“I recommend to my patients that if they haven’t had what feels to them like a normal period—whatever their usual length and flow—within a month, they should take a pregnancy test, just to be sure,” says Dr. White. And the same goes if a person hasn’t had a period at all, of course.

Are there any long-term implications of using EC?

Neither hormonal EC nor the copper IUD have been around long enough to truly determine the long-term impact of using them. But because your fertility bounces back pretty soon after taking hormonal EC, Dr. White doesn’t believe they have any lasting impact on one’s system. “If you’re not on hormonal birth control, your natural hormone levels quickly return to normal after a single dose of oral EC,” she says. “After your next period, your cycles will not be irregular from the EC, and you’ll return to your usual cycling patterns.”

As for copper IUDs, most women choose to keep them in their bodies for months or years (they can last up to 10 years). Integrative physician Felice Gersh, MD, fears that the copper could cause inflammation in the uterus, although this is just a theory. However, available data shows IUDs of all kinds to be extremely safe.

Next time you’re facing that worst-case scenario, just know that there is literally a plan B out there. Breathe, girl. You’ve got this.

This is how long emergency contraceptive pills stay fresh, in case you want to stock up and be prepared. Or if this whole conversation made you want to get an IUD, like, now, here’s what to expect from women who’ve been there.