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 using countdowns and giveaways to drive demand.
Experts warn these tactics pose serious health risks.
Retatrutide remains unapproved anywhere in the world.
Other prizes include Glow pens and melanotan II, which lack UK approval.
UK law restricts weight-loss injections to prescription-only supply.
Unlicensed drugs cannot be legally sold or advertised.
Some sellers disguise drug sales as fitness or coaching programmes.
Researchers say this marketing trivialises risks and bypasses safeguards.
Telegram and Meta state that their platforms ban illegal drug sales.
