Cases of women's drinks being spiked with drugs by men intent on "date rape" are not as common as is widely believed, scientists say.
They believe that if a drink is spiked, it is usually with more alcohol.
Environmental Science and Research forensic manager Wayne Chisnall said the institute had received 162 samples for analysis in the past two years from police investigating sexual assault cases.
None had shown any trace of known date-rape drugs, such as gammahydroxybutyrate (known as GHB or Fantasy) and ketamine.
But scientists dealing with the samples reported that high levels of alcohol were found in a large number of samples.
Twelve samples had shown traces of sedatives but half of those people admitted taking the drug themselves.
Of the remaining six affected, two were men, which proved drink-spiking was not limited to women.
But that did not mean that drink-spiking did not happen, or that those who complained to police had not been drugged, Mr Chisnall said.
Some drug-rape drugs could leave the bloodstream in about four hours and urine in 12 hours.
Often the decision to act was not made until the drugs had metabolised.
ESR scientists did not believe drink-spiking was an urban myth, but the feeling among those who analysed samples was that if drinks were spiked, it was probably with more alcohol.
ESR is the sole agency used by police to analyse samples from people claiming to be victims of drink-spiking, or who may have blacked out or had an unusual reaction.
Research by the Western Australia Chemistry Centre - a Government agency - showed that out of 44 samples supplied by police for testing over 18 months, none showed any trace of drugs that would suggest drink-spiking.
Detective Senior Sergeant Simon Perry, of Wellington CIB, said anecdotal evidence showed that cases of drink-spiking were on the rise, but they were hard to prove.
"Actual occurrences are very difficult to verify," he said. "Where a drug is found as a result of testing, it is in fact a bonus."
The number of drink-spiking cases reported nationally to police each year was not available.
Mr Perry urged anyone who believed their drink had been spiked to get a blood or urine test as soon as possible. Police could organise this.
Drug Rape Trust chairwoman Jenny Fenton said the prevalence of drink-spiking was not overstated.
But people also had to be aware of their tolerance of alcohol and its effects, which could be mistaken for being drugged.
- NZPA
Date-rape druggings rare, scientists find
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