How Effective is Plan B? 12

The majority of women have heard of Plan B, however it’s often simply marketed as this thing that you take anytime you’ve had unprotected sex or a contraceptive failure—that is if you don’t want to become pregnant—but how effective is Plan B really? What is Plan B and how does it work? Are there side effects? What are they? Fewer women know the answers to these questions. Luckily, to fully understand how effective Plan B is you need to understand what Plan B is and how it works so you learn the answers to all these questions.Plan B effectiveness, how effective is plan b

So, let’s start at the beginning…

What is Plan B?

Chances are if you’re looking up Plan B effectiveness, you get that it’s a pill that helps prevent pregnancy, but to be more accurate, Plan B is a large dose of levonorgestrel. Levonorgestrel is a progestin that can prevent pregnancy primarily by preventing ovulation, but it may also prevent implantation.

How does plan B work?

Progesterone is a hormone that’s always present during your menstrual cycle. It maintains your uterine lining after ovulation. If you become pregnant, progesterone rises to cease ovulation and keep you from getting a period. Plan B essentially mimics pregnancy by delivering a large dose of progesterone (levonorgestrel mentioned above) so that the body already “thinks” it’s pregnant, doesn’t ovulate, and instead continues to thicken the uterine lining. As this large dose dissipates, withdraw bleeding occurs which usually resembles a period.

How effective is Plan B?

Plan B effectiveness really hinges on when it’s taken. The manufacture may tout it prevents 7 out 8 pregnancies, but realistically that’s likely only with perfect timing. Yes, Plan B must be taken within 72 hours, but there’s more to that story.

If Plan B is taken early in your cycle, it probably does have the suggested upwards of 89% effectiveness, but closer to mid-cycle, probably not, and after ovulation? It’s nearly a pointless measure. This is because you can’t prevent ovulation if it’s already happened.

After ovulation, all Plan B does is work to thicken the uterine lining more to prevent implantation. This means the later in your cycle it’s taken the less effective it becomes.

So, when should you take Plan B, if at all?

The reason it’s generally recommended to take Plan B at any time if you’ve had unprotected sex and don’t wish to become pregnant is because not all women know when they ovulate. Honestly, if they did they wouldn’t need Plan B, because they would know if the sexual act occurred during a fertile time.

Pregnancy is actually only possible about one week out of the month. You have the viability of sperm at about 5 days, and the lifespan of an egg at around 24 hours. You can read more about your chances of pregnancy here, but long story short, in general, sex just before or just after a period is very unlikely to result in pregnancy. Whereas, sex mid-cycle has a higher chance.

Sadly, not all women ovulate mid-cycle. You can’t just assume if the sex is properly timed you won’t become pregnant and don’t need Plan B. It is actually possible to become pregnant from sex just after your period (when Plan B would be most effective), and at mid-cycle when you’re most likely to become pregnant, Plan B will at least hinder implantation by thickening the uterine lining and subsequently causing withdraw bleeding to thin it.

The only situation where we would say you’re probably just suffering side effects for no reason by taking Plan B is when the sex occurred in the final week before your period. Why?

First, ovulation has likely already occurred by a long shot. There probably is no chance of pregnancy to begin with. Second, there is very little time to thicken the uterine lining. Additionally, if you are basal body temping and know when you ovulate, there is no reason to take Plan B unless you are in a fertile period.

Speaking of side effects…

Plan B Side Effects:

Side effects of plan B are basically a ramped up version of PMS, but may also mimic pregnancy symptoms. These include nausea, fatigue, feeling hot, discharge changes, bloating, cramping, and gas. This is because, as stated back there on how Plan B works, you’re creating a hormonal situation akin to pregnancy.

However, the most common Plan B side effect is irregular bleeding. Enough so you can read an entire page on this topic here.

I hope this has helped answer your questions about how effective is Plan B, but if not, we welcome comments and questions here at Life with Gremlins.

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My boyfriend and I had unprotected sex around 5 in the morning on June 6th. I took an ovulation test to see if I was ovulating and it was positive. I took plan B that night around 7pm. Today it is June 7th and I went to the bathroom and wiped and I noticed fertile discharge like what happened when you’re ovualting. It was clear and stretchy. Does this mean that I’m ovualting anyway and could be pregnant now? Or could that be some sort of side effect..


Hi,I need a big help, my girlfriend thinks she’s pregnant and wants to take a test soon. I told her last month she was also late about 4-5 days so she might get it late this month. She was late because she took a plan b on the same week her period was due last month. She has a app telling her period was due already 4 days ago and we had sex last week on the 21st with a condom. But on that day I noticed she had a very creamy thick fluid around her vagina so I was… Read more »


My girl friend took the plan b pill two days before her period (12/22) Condom ripped but I pulled out but I got her the pill 1 hour later Unfortunately the condoms I got were just not the best and we had intercourse and whoop ripped again But i also pulled out, this happened after three hours she took the pill. Me and her decided since she took the pill we didn’t need another one plus her period was coming. Her peroid was due today (12/24) and still no sign and I’m really worried because of the precum. So My… Read more »