When I started to investigate the trade in slimming pills, I knew I would encounter a sprawling international and unregulated marketplace - but I did not expect to be offered heroin.

It was just one of the shocks waiting in the alarming world of banned drugs and potentially lethal side effects.

With millions thinking about how they'll look on the beach, diet pills can look like an attractive shortcut.

What we have discovered should make anybody think again.

Watch the full report of what we found here:

Our findings

  • When we ordered the diet drug DNP we were actually sent Clenbuterol. This is a banned medicine linked with increased risk of heart attack. It had impurities that could make the effect even stronger.

  • We ordered and received, Sibutramine - withdrawn in the UK 5 years ago - it is linked with heart attacks and strokes, seizures, bleeding and jaundice.Worryingly, there was more than double the amount stated on the packet in each pill. It is marked as prescription only but was sold to us without. Oddly one of the side effects is "increased appetite".

  • We got Ephedrine - in a form that is prescription only. It is not licensed for weight loss and is linked with heart problems and paranoia in long term use.

  • We ordered Phentermine - but our lab analysis showed it was not what we got. Instead we received a dietary supplement of Phenethylamine - followed by the offer of "heroin and hash".

An inquest into Eloise Parry's death, thought to be linked to DNP, is due to open today. Credit: West Mercia Police

The criminal dealer even sent me a photo of the heroin he was offering.

The email we got says: " I sell only pure heroin and hash online I am looking for fresh new good clients".

This is clear evidence of diet pill websites being used as a front for the sale of hard drugs.

Other pills showed how global this dangerous trade is.

The Sibutramine marked "Slimex " was made in India, sent to us from Hong Kong and disguised along the way as "plastic beads".

A photograph of the heroin that was offered. Credit: ITV News
The packet marked 'plastic beads' actually contained diet pills. Credit: ITV News

Neal Patel from The Royal Pharmaceutical Society, which helped throughout our investigation, said: “These results show that buying drugs for weight loss on the internet is like playing Russian Roulette with your health.

"You don’t know what you are buying and the products can be very dangerous, even lethal.

"Research is ongoing into medicines for weight loss but there’s no legal, safe, breakthrough tablet. Talk to a health professional like a pharmacist or doctor to get proper advice about how to lose weight safely.”

Ahead of its general release, ITV News has been given advance access to a new official video designed to warn people about the dangers of DNP.