Women have been warned that widely-used morning-after pills
might not prevent pregnancy if they weigh more than 70kg.
Thousands of women in New Zealand take the pill, but the
Ministry of Health has issued a precautionary alert after
overseas research raised concerns over the emergency
The ministry is reviewing the research before deciding on any
These could involve warnings on information sheets or
The average weight of women in New Zealand is over 72kg.
About 16,000 prescriptions were given out last year for
Postinor-1, the sole state-funded emergency contraceptive
pills - but it and two other brands, Next Choice and Next
Choice Arrow, can also be bought from pharmacists.
The ministry notes that irrespective of a woman's weight, the
pill - which is intended to be taken within 72 hours of
unprotected sexual intercourse - may not always prevent
pregnancy. The sooner it is taken, the more likely it is to
Family Planning says the pregnancy rate after emergency
contraceptive pill (ECP) use among women who are technically
obese - those with a body mass index over 30 - "is the same
as for women who don't take an ECP at all".
It says the research - which has prompted reviews in several
countries - found a pregnancy rate among obese women who used
levonorgestrel (the active ingredient in Postinor-1) or
another emergency pill was three times that of women whose
BMI was under 30.
"Women who come to a Family Planning clinic needing emergency
contraception are given the option of a post-coital IUD [the
Multiload copper intra-uterine device] instead of the
emergency contraceptive pill because it is more effective,"
the organisation says in its Forum newsletter.
"... when used as emergency contraception [it] is more than
99 per cent effective no matter how much a woman weighs.
Also, if the woman chooses to keep the IUD in place, it
provides up to five years of highly effective contraception."
Family Planning's medical director, Dr Christine Roke told
the Herald: "We've been encouraging women, particularly the
heavier ones, to consider having the IUD, but most feel more
comfortable with taking the pill."
She said it was not known why the emergency contraceptive
pill was less effective in heavier women.
It was thought that it took longer for hormones in heavier
women to reach the required level.
"While that doesn't matter when you're taking a contraceptive
pill each day, it matters for emergency contraception because
you want to get the levels up as soon as possible."
Physician and clinical pharmacology fellow Dr Jenny Robinson
wrote on Australian website The Conversation that although
the concerns raised by the research were serious, the small
number of overweight and obese women in the studies and the
low number of pregnancies meant "we should be cautious in
applying the results too broadly".
In the research, 1731 women took levonorgestrel pills and 38
became pregnant, while 1714 women took ulipristal acetate and
22 became pregnant.
Obese women were 13.6 per cent of the study group, and
overweight women 21.6 per cent.
Morning-after pill warning
• Researchers discover widely-used emergency contraceptive
has higher chance of failure if woman weighs more than 70kg
• Health ministry issues alert, and Family Planning says it
offers another option 'because it is more effective'