Emergency Contraceptive Pill (ECP)

All about the ECP

The emergency contraceptive pill in New Zealand is made of levonogestrel 1.5mg.  It can be 93-95% effective for preventing pregnancy in women who are under 70kg.  If you are over 70kg you should take 2 of the tablets. 

A crucial point: if you take it AFTER you have ovulated is it highly likely NOT to work.  ie if you have ovulated it is much better to use a copper IUD as contraception.  The main mechanism of action of the ECP is to delay ovulation.  It is most effective the quicker after unprotected intercourse that it is taken too. 

When to use the ECP:

• Within 72 hours after unprotected sex
• Before ovulation in the menstrual cycle
• As soon as possible for best effectiveness

Side effects:

• Nausea and vomiting (most common)
• Abdominal pain and cramping
• Breast tenderness
• Dizziness and fatigue
• Headache
• Irregular bleeding or spotting
• Changes in timing of next period

If you vomit or have diarrhea:

• If you vomit within 3 hours of taking the ECP, you need to take another dose
• Take anti-nausea medication before the second dose if needed
• No specific guidance for diarrhea, but if severe, consult a healthcare provider

Additional notes:

• Take with food to reduce nausea
• If your period is more than 5 days late, take a pregnancy test
• Seek medical attention for severe abdominal pain (possible sign of ectopic pregnancy)

A deeper dive:

• Mechanism of action: The primary way ECPs work is by delaying or preventing ovulation1. If ovulation has already happened, the ECP cannot prevent it retroactively.
• Timing is crucial: The effectiveness of the ECP decreases significantly the longer you wait to take it after unprotected sex, partly because it may be too late to prevent ovulation.
• Difficulty in determining ovulation: It's challenging for most women to know exactly when they ovulate, which is why it's recommended to take the ECP as soon as possible after unprotected sex, regardless of where you think you are in your cycle.
• Alternative for post-ovulation: The copper IUD is the only form of emergency contraception that remains effective even after ovulation, as it can prevent implantation.

This information underscores the importance of taking the ECP as soon as possible after unprotected sex, and not relying on estimations of ovulation timing when deciding whether to use emergency contraception.  It is also important to think about other forms of contraception.  There are short acting and long acting ones.  These are generally more effective than the ECP too.