Among the victims, 84 percent had drunk alcohol before the assault, while 59 percent tested positive for drugs. The seven-year review analyzed 264 blood and urine samples. The average blood alcohol content was 1.7 promille.

"You're close to unconscious with such a high blood content level, especially young girls who aren't used to drinking alcohol regularly," medical chief Cecilie Hagemann told NRK.

Hagemann analyzed blood and urine samples from women who sought help at the rape victims unit at Trondheim's Saint Olav hospital between 2003 and 2010.

"We found a blood alcohol content level of 1.2 promille once they reached the clinic," said Hagemann, whose research was part of her doctoral thesis.

"If you trace that backwards to the time of the assault, the promille would have been 1.9. It's a very high level, especially when you take into consideration that many are young women," Hagemann told NRK.

She added that research into the attackers would also be useful, as previous studies have shown they are at least as likely as their victims to have consumed alcohol or drugs before the assault.

Oslo-based medical chief Henriette Waitz added that victims should seek help immediately, and not sleep off their intoxication first.

"They should not go home to sleep it out, because you lose some possibilities both to help them and to secure forensic evidence," Waitz said.

"You may want to collect yourself before asking for help, but it is very important to get help even if you are still drunk."