Hidden-market sellers promote unlicensed weight-loss drugs through WhatsApp and Telegram giveaways.
They offer injectable medicines such as retatrutide as competition prizes.
The Guardian found groups urging users to enter within 24 hours.
Experts warn these tactics create serious health risks.
One group promoted prizes including retatrutide, Glow pens, and melanotan II.
None of these injectable products hold UK approval.
UK law allows weight-loss injections only with valid prescriptions.
Unapproved drugs cannot be legally sold or advertised.
Another seller disguises drug sales as fitness coaching programmes.
Researchers say these promotions misuse marketing pressure and bypass safety rules.
