Doctors says some schools and parents are doing better than others when it comes to informing teens about contraception.
Most 14- to 18-year-olds interviewed by Otago researchers knew little about long-acting implants and IUDs - despite these being 22 times as effective as the pill.
College of GPs medical director Richard Medlicott says if doctors aren't fully informing patients, they may need to lift their game.
"Have a talk to young people about this - they don't want to get pregnant, and we don't want them to get pregnant, so we should be helping them the best way we can."
Dr Medlicott says doctors can take something from this research.
"I was a little bit surprised, really. I thought there would be more understanding. I suspect that some schools and parents are clearly doing better than others."
He says they'd like to see the intra-uterine device Mirena more widely funded. Mirena and other levonorgestrel-releasing devices have a failure rate of around only 0.2 percent, compared to the pill's 7 percent and condoms' 13 percent. Mirena and similar devices can last between five and seven years, once implanted.
Dr Medlicott says long-acting, removable contraception is very effective, and they'd like to see it used more.
"Clearly condoms have got advantages in terms of reduction of STIs, but they're not as effective for contraception. If people are going to see doctors and they're not being fully-informed, maybe we need to lift our game a bit."
The researchers' findings were published on Friday in the New Zealand Medical Journal.