Women who claim to be victims of 'date-rape' drugs such as Rohypnol have in fact been rendered helpless by binge-drinking, says a study by doctors.
They found no evidence that any woman seeking help from emergency doctors because their drinks were allegedly spiked had actually been given these drugs.
Around one in five tested positive for recreational drugs while two-thirds had been drinking heavily.
The findings further erode the theory that there is widespread use of Rohypnol and GHB, another drug said to be favoured by predatory rapists.
Last month a personal safety campaigner claimed that Rohypnol had never been used to assist a sexual assault in the UK. Doctors carrying out the latest study at the Wrexham Maelor Hospital said it was far more likely women were claiming their drinks had been spiked as an "excuse" for binge-drinking.
The 12-month study was based on 75 patients - mostly women - treated in casualty who told doctors their drinks had been tampered with in pubs or clubs.
But tests for drugs such as Rohypnol, GHB and ketamine found nothing, says the study published in the Emergency Medicine Journal.
It showed 65 per cent of women had 160mg of alcohol in their blood - twice the 80mg drink/drive limit - and a quarter were three times over the limit. Although all the patients denied taking drugs such as cocaine and amphetamine, one fifth tested positive.
Researcher Dr Hywel Hughes, an associate specialist in A&E said: "This study confirmed our suspicion that most of the patients with suspected drink-spiking would test negative for drugs. No ketamine, GHB or Rohypnol was found in the samples which suggest they are not commonly used to spike drinks.
"There has been a lot of media coverage in recent years, mainly focusing on just a few substances including Rohypnol and GHB, which has led to the perception that drinkspiking is a widespread practice. But most patients allegedly having a spiked drink tested negative for drugs misuse.
"Claiming their drink has been spiked may be used as an excuse by patients who have become incapacitated after the voluntary consumption of excess alcohol."
Dr Hughes said some women might have felt ashamed at ending up in casualty. "There seems to be greater awareness about the dangers of binge-drinking, which is where the emphasis should stay," he added.
Last month Julie Bentley, chief executive of the Suzy Lamplugh Trust, said many women fall victim to sexual assaults after being plied with alcohol. Commenting on claims that Rohypnol had played a part in sex attacks, she said: "As far as I am aware, there has never been a case of Rohypnol in this country found."
In the light of the latest research, Dr Peter Saul, a GP in Wrexham, said: "There had always been a suspicion that people would say that their drinks had been spiked when perhaps they had misjudged how much alcohol they were taking.
"If you go home and your parents are there, and you are vomiting on the path, and you come in in a terrible state, you get sympathy if you say, 'My drink was spiked'.
"You don't get sympathy if you say, 'We spent too long in the bar'."
He added: "The message has to be: be careful - not just about having your drink spiked - but how much alcohol you have."