The Plan B pill

The American morning after pill


The plan B pill is an American branded morning after pill. Its UK equivalent is Levonelle. Each brand of pill contains 1500 micrograms of levonorgestrel which is its active ingredient. Whilst it is called the morning after pill it is, in fact, most effective if taken as soon as possible after unprotected sex. The statistics for its efficacy are as follows:

If taken within 24 hours of unprotected sex - 95% effective

If taken between 48 and 72 hours of unprotected sex - 61% effective

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It is worth considering the use of Plan B One-Step if you are not using any regular form of contraception and any of the following events occur :

  • The condom fell off or split
  • The diaphragm slipped out of place
  • Two or three birth control pills were missed consecutively
  • You forgot to insert your ring or apply your patch
  • Your partner didn’t pull out in time
  • You have another reason to believe that your regular contraception may have failed. For instance, if you had suffered from a stomach upset at some point in your cycles and may have ‘expelled’ the birth control pill from your system
  • You were forced to have unprotected sex

It is worth noting that the morning-after pill is not as effective as regular forms of contraception


How does the Plan B pill work

Levonorgestrel, which is a synthetic hormone that acts in a similar way to progesterone, is the active ingredient in the plan B pill. This ingredient operates to prevent pregnancy beginning in several ways

  • The release of the egg from the ovary is either delayed or prevented completely

  • Should the egg become fertilised, it causes changes in the lining of the uterus that prevents the fertilised egg from implanting


How to take Plan B One Step

Plan B One-Step can be bought over the counter in America and the English equivalent, Levonelle is available without prescription over the counter in pharmacies, from sexual health and contraception clinics as well as from abortion clinics.

It should be taken as soon as possible after unprotected sex has taken place, preferable within 24 hours but can be taken within 5 days.

As time is of the essence in terms of taking the pill swiftly, it may be worth holding a supply in the medicine cabinet. However, it is far more advisable that a regular, more reliable form of contraception is considered rather than relying on emergency contraception.


Side effects of Plan B One Step

Although many women will not experience side effects from emergency contraception, there are some that will.

Prospective side effects include:

  • Nausea and vomiting. If you vomit it is important that you contact your health care professional to find out if it will be necessary to repeat the dose
  • Abdominal pain
  • Fatigue
  • Headache
  • Menstrual changes
  • Dizziness
  • Breast tenderness

Levonorgestrel may cause some bleeding but this should stop before the next period arrives. Your next period may also be heavier or lighter than usual and it may appear later or earlier than normal. If your period hasn’t arrived within three weeks it is important that you take a test to confirm that you are not pregnant 


Will Plan B One Step affect my fertility?

There is absolutely no evidence that Plan B One-Step will have any effect on your becoming pregnant in the future.  Neither is there any evidence to suggest that it will have any effect on your likelihood of miscarrying in future pregnancies?

There is no limit to how many times you take Plan B


What if you are pregnant when you take Plan B?

If you take Plan B while you are pregnant it will not affect the pregnancy.   There is no evidence to date that the pill will affect the growing fetus.


Who can take Plan B?

If you are able to take the contraceptive pill without a problem then you will almost definitely be able to take Plan B pills.


Plan B and overweight women

Plan B One-Step is accepted in the US as being the most cost-effective and convenient form of emergency contraception available to women.

However, it has a high failure rate in women who are overweight.

In a large European study testing the effects of levonorgestrel 1.5 mg (Plan B), it was shown that its potency drops in women over 165 pounds and is non-existent once a woman gets to 175 pounds.

Theories exist as to why increased weight leads to decreased efficacy of levonorgestrel including the extra dilution of the drug in larger blood volumes, hormones becoming tucked away in fat cells or the system of a heavier person metabolising the drug in a different way but none of these theories have been proven.

It may simply be that a heavier person needs a larger dose but to do this in practice would be prohibitively complicated.

Fortunately, the alternative EC pill Ella (EllaOne in the UK) appears to be just as effective in heavier women.


Alternative forms of emergency contraception

The other emergency contraceptive pill available has the active ingredient ulipristal acetate and is sold as Ella in the US and EllaOne in the UK.  It is more effective than Plan B and Levonelle.

Ella maintains the same level of effectiveness if taken up to 5 days after unprotected sex. It is a better choice if you have waited more than 24 hours to seek emergency contraception. Its effectiveness does not diminish if given to someone with a BMI over 25

Insertion of a copper intrauterine device (IUD) can be carried out up to five days after ovulation; this will prevent a pregnancy from occurring. This is the most effective form of emergency contraception being 99% effective in preventing pregnancy.


Is Plan B One Step the same as the abortion pill?

Plan B One Step is NOT an abortion pill. It is a form of emergency contraception that prevents unwanted pregnancy.


What else should I know?

  • The morning after pill does not protect from sexually transmitted infection and so it is advisable to always use condoms
  • If you are currently using the pill, continue or restart your course on the same day as you take plan B and use condoms as back up contraception for the next seven days
  • If you are not currently using regular contraception, speak to your health care provider about the options



It is important to be clear about the morning after pill. It is a form of emergency contraception that prevents pregnancy from occurring by delaying or stopping ovulation and preventing the egg from becoming implanted in the wall of the uterus; it does not terminate an existing pregnancy. 

To end an early pregnancy requires the abortion pill. If you are looking to terminate an early pregnancy it will be necessary to seek help and counseling from a professional trained in this field. For further information and advice contact your GP or one of the organisations that specialise in abortion such as the NHS, BPAS, or Marie Stopes.

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