Pub-goers are being warned alcohol is the main drug used in "date rape" attacks.
About a third of sex attack victims had been drinking excessively
Police in Southampton say that over the last year about one third of women and several men who claimed to have been the victims of rape or serious sexual assault in the city had been drinking to excess.
The warning comes as the government is being urged to run a national Christmas campaign about the dangers of drinks being spiked.
The number of people who claim to have been sexually assaulted after drugs were put in their drinks rose to 1,000 this year, the Roofie Foundation said.
The group, which helps victims, said a media campaign should be run alongside the annual drink-drive messages.
Hampshire Constabulary has already said it will be launching a poster campaign in clubs and pubs across the county urging people to take extra care to prevent their drinks being spiked with date rape drugs.
But officers warn that excessive drinking itself poses the biggest danger to women in particular.
Detective Inspector Nigel Oliver said: "Alcohol is the most common date rape drug and much, much more commonly used than the relatively rare Rohypnol or GHB.
"In many cases, victims have been so drunk as to be unable to fully recount what has happened to them.
"This can severely hamper the investigation and subsequently can lead to difficulties proving the offence in a court."
Police are advising women in particular to stay in groups when on a night out, book taxis in advance from a listed, licensed company and to keep drinks in view at all times.
Out of 30 police forces contacted by the BBC, two-thirds said they were running their own Christmas campaigns.