The 'King Kong' of weight loss jabs is now available to buy privately in Britain. 

Clinics are charging around £40 for a week's supply of Mounjaro, or tirzepatide.

Patients taking it can expect to lose up to 20 per cent of their body weight, data suggests.

Anyone with a BMI above 30 — the technical classification for obesity — can get a private prescription.

Tirzepatide supplies have also reached the NHS. However, doctors are limited as to who they can give it to. 

Under current guidelines, only people with type 2 diabetes, who do not have the condition under control, are eligible to get it on the NHS. 

Health officials are considering expanding its usage for weight loss on the NHS, where it will cost the standard prescription rate.

The once-a-week drug, injected under the skin of the stomach, thigh or upper arm, was approved for use by drug chiefs in November last year.

However, it has not been available because of huge global demand.

Mounjaro will provide an alternative to Wegovy — or semaglutide — which has also been in short supply due to overwhelming demand.

Simple Online Pharmacy, one firm which is now offering Mounjaro privately, says it has 80,000 patients wanting to start treatment. 

According to its website, a month's supply is expected to cost £42 a week.

Another clinic, My London Pharmacy, is selling it at £119 for a starting dose.

Tirzepatide, developed by the US pharmaceutical firm Eli Lilly, works by suppressing two appetite-regulating hormones, making people feel fuller for longer while also making them experience fewer food cravings. 

The jab will be supplied in a four-dose pen branded as KwikPen, which provides a month's treatment when used once a week.

It was previously only available in single doses.

Patients in the US are already able to get the jab for weight-loss 'off-label' from some doctors, with many sharing their unbelievable transformation. 

One overweight man claimed the medicine helped him shed up to 100lb (45.4kg).

Before-and-after pictures show the transformation of Matthew Barlow, a 48-year-old health technology executive living in California.

He began using the drug last November. At the same time, he also changed his diet and lifestyle, as recommended. 

'Psychologically, you don't want to eat. Now I can eat two bites of a dessert and be satisfied,' he said.

Meanwhile, one TikTok user called Emily, claimed she had lost 140lb (63.5kg) since startling on the weight-loss injections.

'The incredible amount of joy that is in me when I look in the mirror now is insane,' she said. 'I used to cry at myself in the mirror. Now I feel like one of the cool kids.' 

Like all drugs, Mounjaro is not without side effects.

The MHRA has warned the drug may effect how well the contraceptive pill works in obese or overweight female patients. 

Other potential side effects include nausea, diarrhoea, vomiting — which usually goes away over time — and constipation.

Low blood sugar is also 'very common' in patients with diabetes, the agency added. 

One trial involving 900 participants also found a fifth suffered from nausea and diarrhoea, and about one in ten reported vomiting or constipation.

Other people taking the drug outside clinical trials have reported experiencing hair loss while taking Mounjaro. 

There has also been a suggested link to an increased risk of cancer from the jab.

The European Medicines Agency said this year that research on rodents has suggested the artificial hormones packaged in tirzepatide could raise the risk of medullary thyroid cancer.