Questions are being raised about the effectiveness of emergency contraception for women weighing more than 70kg.
International research shows that the form of contraception known as the morning-after pill is less effective for women who weigh more than 75kg and ineffective for those in excess of 80kg.
Medsafe, which is reviewing the research, issued an early warning in February to the medical profession saying recent publications have indicated the active ingredient in the pill might not be effective for women heavier than 70kg. The average weight of New Zealand women is 72kg.
Most of the 150,000 pills taken each year can be bought over the counter at pharmacies.
Family Planning's national medical adviser, Christine Roke, told Nine to Noon it has given advice to pharmacies about the research.
"We haven't set a specific weight," she says. "We've just presented that information, and that they should be advising them to see a doctor for an IUD - but also giving them that emergency pill then, as we would, in case the woman changes her mind in between times."