Excitement around the creation of a new drug, especially one showing early promise in clinical trials, is often celebrated by those developing it.
But new weight-loss drug retatrutide has become a headache not only for Eli Lilly, the pharmaceutical company behind it, but for regulators in the UK and around the world.
The jab has not yet been approved for human use by any regulatory body.
But illicit, counterfeit dupes of retatrutide are currently flooding the black market.
Experts have told the BBC this is one of the first times they have seen copycat versions of an experimental drug, still in the throes of being tested, become so widely available.
Vials purporting to be "reta" as it's become known, are being sold in the UK in gyms, nail and beauty salons, hairdressers, on social media and even by flower sellers on the street.
"The world has gone mad," pharmacist and director of 24 HR Pharmacy, Sehar Shahid says. "People are effectively injecting an illegal drug and thinking it's safe.
"It's become so normalised people openly talk about their dealers, where's best to get it from and post all over social media."
One quick flick through my socials and I can order a batch of a drug billed as retatrutide in minutes - although I would have no proof what it's actually made of, what its effects would be and where it's come from.
Keen users are posting before and after "reta" pics on their TikTok feeds, describing how it has silenced food noise, helped them shed pounds and lose inches, with some saying it's completely transformed their lives.
The problem? Despite positive results in its most recent clinical trials, real retatrutide is still being tested for its safety and efficacy.
Only 50% of drugs in this Phase III stage of testing in the US are eventually approved by the Food and Drug Administration (FDA), so there is no guarantee retatrutide will ever hit the market. The high rate of failure is primarily down to drugs not working as well in large, diverse human populations as they do in smaller early tests, or because they reveal unexpected safety hazards.
And the current, fake versions available may not resemble what's being developed in the safe confines of the laboratory.
Tom Davies says he nearly ended up in hospital after accidentally overdosing on a fake version of retatrutide. He ordered it from a Chinese supplier after friends at his gym recommended it.
"It was horrendous," says the 20-year-old from Brighton. "My body felt so under pressure, I was so bloated, it was like someone had dropped a 20kg weight on my stomach.
"For 72 hours I had really bad diarrhoea and nausea. I thought, if this continues I'm going to end up in A&E."
Tom later realised he had given himself eight times the recommended dose. Depending on what is ordered, copycat retatrutide can arrive needing to be mixed with sterile, bacteriostatic water which requires various calculations.
Dr Nas Khattak, a research doctor based in Chester, has been screening patients for one of Eli Lilly's Phase III clinical trials. He says those sourcing fake versions are in effect behaving as lab rats without any medical oversight.
"If users who buy it online become their own doctor, they're taking a huge risk," he warns.
He says trial participants need to meet strict criteria before they are given the green light to start taking the real drug or a placebo.
"We request their GP record, we make sure that they're emotionally well. They'll have suicide, self-harm, mental health assessments - and this is all done by doctors.
"Then we come back and have a look at the blood tests, have a look at everything, and then we think whether they're suitable or not."
Tom decided to do more research into dosing and, despite the nasty side effects he'd previously experienced, decided to give his fake version of retatrutide another go. After nine months of taking it in cycles, he says his cravings for sugar and junk food have gone.
Pharmacist Shahid warns that just because a fake version of reta works for one person, does not mean it will "work for the next".
The obesity drugs currently on the market - the likes of semaglutide (marketed as Ozempic and Wegovy), and tirzepatide (marketed as Mounjaro) - target just one or two hormone receptors. But, if approved, retatrutide will become the first weight loss medication in the world to act on three, giving it the nickname the "triple G".
The three hormones it mimics are:
GLP-1 - this slows down stomach emptying, signals fullness to the brain to reduce appetite and helps control blood sugar levels
GIP - this enhances insulin secretion and improves insulin sensitivity, and works alongside GLP-1 to help the body process nutrients and reduces hunger
Glucagon - this is the hormone that's novel to retatrutide. It increases resting energy expenditure so the body burns more calories, promotes liver fat breakdown and supports weight loss.
Lisa King has been taking a fake version of retatrutide since July and at one stage, while she was also going to the gym and eating healthily, she was losing 3kg (6lb) a week.
It's also, she believes, helping her manage some of the symptoms of polyendocrine metabolic ovarian syndrome (PMOS). GLP-1s help regulate blood sugar, and some studies suggest these weight-loss drugs can help with some of the problems caused by PMOS, which can bring about extreme tiredness, kidney problems and high blood pressure.
"I'm not sure if it's due to reta," Lisa says, "but my sugar cravings have gone down, my periods have regulated and I've got a lot more energy."
But retatrutide is still in trials. Does this bother her?
"No," she says, "not at all. There are many things that have not been approved.
"If I start to experience any negative side effects I'll just come straight off it."
Other users taking counterfeit versions of retatrutide have reported a range of issues including brain fog, nausea, diarrhoea, a loss of libido and no longer being able to feel any happiness or joy.
Doctors are becoming increasingly worried about the side effects they are seeing amongst users of these counterfeit weight-loss drugs.
Dr Sahira Dar, a GP and chair of the British Islamic Medical Association, says healthcare professionals should ask about black market products "without judgement", so patients feel able to "disclose what they have taken".
Eli Lilly has been developing retatrutide for nearly 10 years. It is now fighting to protect its product and curb the illegal sales which are taking place across the world.
It's taking action against peptide companies, influencers, compound pharmacies which manufacture the fake medication, and wellness clinics. It has reported more than 14,000 websites, advertisements and social media posts it says are illegally marketing the medication.
Eli Lilly says it "continues to work with law enforcement and regulatory authorities to combat black market drugs".
A spokesperson told the BBC: "Any retatrutide available online is unapproved, unverified and simply not worth the risk."
The UK's Medicines and Healthcare Products Regulatory Agency (MHRA) has carried out raids and made several seizures of "products claiming to contain retatrutide" over the past year.
It says there are a number of different routes these products enter the UK and it is working to "disrupt illegal importation and distribution".
But the sales continue.
Prof O'Shea says while we need to "shine a light on the dangers of such black market drugs", we should not "trash this family of medications".
"GLP-1s are a major advance in managing obesity, a major advance in our insight into how the brain regulates cravings and appetite.
"That," he says, "is huge".
For now, there is still a long way to go before retatrutide gets approval anywhere.
Eli Lilly plans to submit its application for US FDA approval early next year. It can take up to a year to carry out a review, so retatrutide would not be legally available in the US until the end of 2027 at the earliest.
In the UK, depending on the approval of the MHRA, it could be on the market by 2028.
