British travellers are apparently 'easy prey' for a South American scam dubbed the 'Goodnight Cinderella'.
The UK Foreign Office went on to warn how dating apps are being used by scammers to 'target foreign nationals in Brazil'.
CNN Brazil reports that the Rio force is currently investigating the case of two British men who were allegedly robbed of $21,000 (£15,000) by three women near Ipanema beach.
Two cell phones were allegedly stolen, and the women allegedly carried out a bank transfer of $16,000 from the victim's account.
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One of the tourists informed officers that he drank a spiked cocktail on Thursday (September 4) after he and a mate met three ladies at a bar. He lost consciousness as they all headed to the famous sandy spot and the three women were later seen getting into a taxi.
When a witness called for help, the pair were taken to hospital and treated by doctors.
What is the 'Goodnight Cinderella' scam?
In recent times, cases of this holiday nightmare have spiked as tourists encounter scheming women who lurk in bars and lace their drinks full of sedatives.
This is happening more and more across the Brazilian city of Rio de Janeiro, with local police claiming these guys are blinded by the glamour, only to wake up with their expensive possessions stolen, including passports and jewellery.
The women lie in wait as the boozers steadily pass out, before helping themselves to their pockets full of cash and mobile phones.
The Civil Police of the State of Rio de Janeiro has since told CNN that authorities are attempting to locate the criminals who stole from the two British men and that the Special Tourism Support Unit is analysing security footage.
One woman - Amanda Couto Deloca, 23, - was arrested last month and charged with aggravated robbery and criminal association. Two other suspects in the case remain at large.
Expert issues warning about 'Goodnight Cinderella' scam
Professor Bayard do Coutto Boiteux of Rio de Janeiro Tourism Ambassadors Association said that the issue typically starts with sex tourism.
"What happens is that some tourists come to Brazil looking for sex tourism, which is completely inappropriate," he revealed to The Sun.
"We are by no means a sexual paradise. When they come here looking for sex tourism, a number of things can happen because there is no effective control by the authorities over prostitution.
"While they're there, seeking sex tourism and talking to these women, they, in reality, in a moment of inattention, slip a pill into their drink. And this pill often causes drowsiness, a state of mind that takes the person away from their daily routine. And then, these women usually go to the place where the tourists are staying, which is also dangerous."
Doubling down on the potential dangers, the professor added: "Never take anyone to the place where you are staying. Never. Not to an Airbnb, not to a hotel."
Topics: Sex and Relationships, Crime, Alcohol, Travel
Dan Seddon