An urgent review is needed to make sure people in England can get weight loss jabs such as Wegovy and Mounjaro on the NHS, top experts warn.
It comes a day after the prime minister said such injections could boost Britain's economy by getting obese unemployed people "back into work".
More than 200 doctors and specialists have now written to the health secretary to say how stretched NHS obesity treatment services face unprecedented demand from patients wanting these drugs.
They warn the injections are only part of what should be a wider package of non-stigmatising care.
They say the government must fix some fundamentals issues in NHS obesity services - chronic underfunding, workforce challenges and unequal access to care.
The letter to Wes Streeting is being sent by the Obesity Health Alliance (OHA), which represents health charities and medical royal colleges, and has compiled a report.
It says some patients can wait up to five years for specialist support, and that some services are so overstretched they have closed their waiting lists entirely.
The OHA wants to see equitable access for obesity treatments, including weight loss injections.
There have been reports of global stock shortages and, currently in the UK on the NHS, the injections can only be offered through specialist weight-management services.
Some patients go private, but many others miss out, warns the OHA.
According to the OHA, about four million people in England are eligible for Wegovy, but NHS projections estimate that by 2028, fewer than 50,000 people a year would get the treatment.
The upcoming approval for the NHS to use another injection, called Mounjaro, dubbed by some as the King Kong of weight loss jabs for how well it appears works in trials, is expected to place even more pressure on the system, the report warns.
Alfie Slade, government affairs lead at the OHA, said: "The new weight loss drugs represent a breakthrough in treatment, giving hope to the millions of people struggling to manage their weight, but they also expose the weaknesses in our current obesity services.
"Without urgent government intervention, we will fail to meet the needs of millions of patients, leading to greater health inequalities."
Despite the benefits, health experts also caution that Wegovy and Mounjaro, which mimic a hormone that makes people less hungry, are not a quick fix. Patients must still exercise and watch what they eat.
Users can put weight back on once they stop the medication.
And, as with any drug, there can be side effects.
Doctors are concerned about the growing numbers of patients they are seeing with complications from taking weight loss drugs bought online without clinical supervision.
In many cases people might not actually be getting what they think they are, which can be very dangerous.
Public health measures to help prevent obesity problems in the first place, such as improving the nation's diet and helping children get enough exercise, are also vital, says the OHA.
A Department of Health and Social Care spokesperson said obesity "costs the NHS more than £11bn a year and it also places a significant burden on our economy".
"With obesity-related illness causing people to take more days off sick, obesity drugs can be part of the solution," they said.
The spokesperson also said junk-food advertising restrictions and a ban on the sale of high-caffeine energy drinks to children would help tackle the "obesity crisis".