The anti-impotence pills help burn off blubber by converting "bad" white fat cells into "good" beige ones, lab tests have shown.
The beige variety of the drug that was identified only last year burns the calories from food, melting the white fat cells which store calories and deposit them around the stomach, 'The Sun' reported.
Experts tested Viagra on mice after research suggested it might be a potential diet drug. They gave them daily doses and fatty grub - and were surprised at how little weight they gained.
"Viagra is not only able to minimise erectile problems, it can also reduce the risks of gaining excessive weight," Alexander Pfeifer added.
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However, they warned against using it as a diet aid until further research confirms the findings.
Viagra was created in Sandwich, Kent, and patented in 1996. It has since been hailed one of the greatest drug inventions for 50 years.
The National Health Survey (NHS) in the UK doles out more than two million prescriptions a year for anti-impotence drugs, including Viagra, the report said.