If you take Plan B (the "morning-after pill") as more than just occasional backup, here's what OB/GYNs want you to know.

Millions of women rely on Plan B, but there aren't stats on exactly how often women are turning to the form of emergency contraception. After all, it's described by the company as a "backup plan" and isn't intended as a first-line of defense. But when I heard a friend casually mentioned that she's taken Plan B upwards of fifty times, I started to wonder: How bad is it *really* to use Plan B as your Plan A?

An informal poll of coworkers and Facebook friends spanning 23 to 30 years old revealed a clear pattern: Everyone had either taken Plan B multiple times themselves or knew someone who had, yet no one knew what was considered "too many times" to take Plan B in one year, or if taking it repeatedly was considered safe. (Some even shared that, at some point, they relied on it more or less as their only form of birth control, taking it multiple times per month.)

We spoke to ob-gyns about the health impacts of using Plan B regularly-read on for everything you need to know.

Is taking Plan B regularly a health risk?

"There aren't health risks to taking Plan B as much as you need," says Lauren Streicher, M.D., clinical associate professor of obstetrics and gynecology at Northwestern Univeristy's Feinbeg School of Medicine. Medically speaking, there isn't any danger, since it doesn't contain estrogen, the hormone that can potentially up your risk of blood clots, Dr. Streicher explains. Plan B contains only a progestin-a synthetic version of the naturally-occurring hormone progesterone found in some birth control pills-which is responsible strictly for preventing pregnancy.

"It's not necessarily bad to use as a regular form of birth control because it is simply a higher dose of a regular progestin-only birth control pill," gynecologist Diana Hoppe, M.D. confirms. And according to clinical management guidelines for OB/GYNs from the American Congress of Obstetricians and Gynecologists (ACOG), "oral emergency contraception may be used more than once, even within the same menstrual cycle."

To ease any potential worries about the ability to get pregnant later on in life, as with any other progestin birth control, there's no reason to think that using it would have any effect on fertility, Dr. Streicher explains.

Still, there's not a lot of data on the safety of emergency contraception pills if used frequently over a long period of time (no studies have been done, considering the obvious limitations), and the ACOG guidelines do note that continued use of emergency contraception like Plan B exposes you to higher total levels of hormones than from ongoing use of your standard birth control pill. While there may not be any clear harm from that, there are still some unknowns, so it's not a great idea to give yourself more of hormones than necessary, says gynecologist Alyssa Dweck, M.D., assistant clincical professor at Mount Sinai School of Medicine.

There are other downsides too. "Irregular bleeding is the biggest complaint I get from people who use this over and over," Dr. Dweck says. Plus, if you take it repeatedly, it may take some time for your menstrual cycle to get back to normal, she says. Nausea is yet another not-so-fun side effect from the higher dose of progestin.

How effective is Plan B at preventing pregnancy?

But what about the whole reason you're taking the morning-after pill in the first place-you know, the whole preventing pregnancy part? Well, as the company states, it's simply less effective than other birth control methods. Compared to the birth control pill or IUD that are around 98 or 99 percent effective, respectively, Plan B prevents pregnancy about 75 percent of the time, if no other birth control was used, says Dr. Dweck. (Of course, this number varies wildly depending on a number of factors including how old you are, where you are in your cycle, and if you took Plan B as a back up after missing one birth control pill or a few, she explains.)

Plan B doesn't become less effective each time you take it, but, "thinking about it statistically, if you keep using it over and over and over again, you're going to eventually be one of those 25 percent who takes Plan B and still gets pregnant," Dr. Dweck says. "The bottom line is, the more you use it, the more chances you're taking that it may fail."

The Bottom Line on Plan B

While the docs all agree there's no clear health danger from taking Plan B even as often as a couple times per month, it's definitely not recommended by anyone as a replacement for regular birth control.

First, there's the practical considerations: Who really wants to worry about tracking down Plan B and spending $40-50 at the drug store every time you have sex? "If someone is having sex even just three to four times a month, you're still talking about a couple hundred dollars a month," Dr. Streicher says.

One of the biggest concerns for docs? If you're relying solely on an emergency contraceptive, that likely means you probably aren't seeing a primary care doctor or OB/GYN, or don't have a trusting relationship with them, says Dr. Hoppe. Whether you go to a family doctor, local clinic, or Planned Parenthood, regular check-ups are a crucial time to talk about the best form of birth control for you, as well as other aspects of vaginal health beyond contraception, like how to prevent STDs (which are on the rise), and how to maintain optimal vaginal health. Bottom line: Plan B is called a "backup" for a reason, and should be treated as such.