Hidden-market sellers promote unlicensed weight-loss drugs through WhatsApp and Telegram competitions.
They offer injectable medicines like retatrutide as prizes.
The Guardian found groups urging users to enter giveaways within 24 hours.
Experts warn these tactics create serious health risks.
Retatrutide remains experimental and lacks approval anywhere in the world.
Other prizes include unapproved peptides and tanning drugs.
UK law allows weight-loss injections only with valid prescriptions.
Selling or promoting unlicensed medicines is illegal.
Some sellers disguise drug sales as fitness or coaching programmes.
Researchers say these practices dangerously bypass medical safeguards.
