New research to find out more about the prevalence of drug-assisted sexual assaults will begin in seven English police forces on Monday.
Drug assisted sexual assaults usually involve spiked drinks
Senior police said there was a lot of hype surrounding so-called "date rape" but no good data available.
The study aims to conduct thorough forensic analysis in all cases where drug or alcohol use is alleged, even when charges are not being pressed.
Victims are being urged to help by making early complaints to police.
The six-month project involves the Metropolitan Police Service, and Greater Manchester, Northumbria, Lancashire, West Midlands, Leicestershire and Derbyshire forces.
The initiative was first announced in July.
Specially trained sexual offence liaison officers (Solos) will ask complainants for their consent to take part in the research.
If permission is given, questionnaires and samples will be taken.
Existing sexual assault referral centres in each area will be used.
The project leader and head of Derbyshire CID, Det Ch Supt David Gee, said his team wanted scientific results that would highlight the extent of the problem.
"There is currently no empirical data of this type of offence. There is a lot of talk and a lot of hype surrounding the issue of so called "date rape" and drug rape in the media.
"It's important for us to know if drugs are being used in this type of offence and, if so, which types so we can effectively tackle the problem through both drug enforcement and adequate warnings to the public."
He said previous research suggested alcohol was the still most common way to spike drinks.
Det Ch Supt Gee also warned on the potential dangers of relying on high street drink spiking detection devices, saying they were not 100% accurate.
People should take precautions while out drinking, he said.
Safeguards include going to the bar with anyone who offers to buy them a drink; never leaving a drink unattended; and drinking out of bottles, keeping their thumb over the top.
If an unattended drink appears to have more liquid in it or to have changed colour or taste, it should be reported to the management of the premises concerned, he added.
The study is being carried out under the guidance of the Association of Chief Police Officers' steering group on rape.