Most patients who believe they have had their drinks spiked test negative for drugs, research at Wrexham Maelor Hospital has found.
So-called "date rape" drugs include ketamine, Rohypnol and GHB
The study aimed to assess the scale of drink-spiking in the area and identify problems at specific clubs and pubs.
But the year-long investigation of hospital patients found fewer than one in five showed any trace of drugs.
The research concluded the patients' symptoms were more likely to be the result of excess alcohol.
So-called "date rape" drugs include ketamine, Rohypnol and GHB.
During the 12-month study there were 75 alleged cases of drink-spiking.
Patient samples were analysed for alcohol and drug levels, and information was recorded about where the alleged spiking had happened.
The alleged incidents took place in 23 different locations, although two locations accounted for 31% of the cases. Only 14% of the patients had informed the police.
The research, which was published in the Emergency Medicine Journal, found 65% were twice the legal drink-driving limit, and 24% were three times the drink-drive limit.
The investigation looked at 75 cases of alleged drink-spiking
Dr Peter Saul, a GP in Wrexham, said the report's findings "should not belittle the danger" people faced either from drink-spiking or drinking too much alcohol.
He told BBC Radio Wales: "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 'oh, my drink was spiked.'
"You don't get sympathy if you say 'we spent too long in the bar'."
Dr Saul said the report did not make it clear if people's drinks had been spiked by alcohol, as opposed to drugs.
He said: "It could explain the figures of people with very high alcohol levels."
He added: "The message has to be to be careful, not just about having your drink spiked but the total amount of alcohol you have when you are going out for the night."
Professor Jonathan Shepherd is a Cardiff-based surgeon who has pioneered a method for hospital casualty units to compile statistics on the drink-related assaults.
He told the same programme: "It really puts to bed a myth that's very widely held that drinks are spiked when in reality they are not."
Prof Shepherd's research has included breathalysing up to 900 late-night drinkers in Cardiff city centre.
He said: "There is certainly a sizeable minority who are drinking huge amounts of alcohol.
"For all of us, it's a cautionary tale - we ought to be deciding beforehand how much are going to drink on a night out."
However, Prof Shepherd acknowledged that drink-spiking was a still a risk, which he said was easier to prevent by drinking from a bottle rather than a large glass.
Dr Hywel Hughes, who led the study at the Wrexham Maelor Hospital, said the survey's results should not obscure the risks of drink spiking, as one-in-five people tested showed signs of "drugs of abuse".
He said: "The bigger picture is probably the alcohol but spiking does go on, so people do need to take precautions against that."