The hormone replacement therapy (HRT) supply crisis must be resolved quickly because “so many women” are experiencing distress and some are risking serious side effects by using medication prescribed to others, the UK’s most senior GP has warned.

There have been acute shortages of some HRT products, which are used by about 1 million women in the UK to treat symptoms of the menopause. Some women have turned to the black market or are meeting up with other women in carparks to buy, swap or share medicines.

Prof Martin Marshall, the chair of the Royal College of GPs, told the Guardian that action was required urgently to resolve the crisis. “The college is concerned to see supply issues around the provision of HRT, and we understand the distress this is causing to so many women,” he said. “It is really important that this is resolved as quickly as possible.

“We are hearing that the supply issue is specific to England, as there has been a big rise in the demand for oestrogen, particularly transdermal, we use. There is not the same problem with the supply of some of the other oral preparations which are appropriate for many women in the UK and give good symptom relief.”

Thousands of GPs across the country are being briefed about which products are available to enable them to help women who may need to be prescribed a substitute, Marshall said.

However, he also raised concerns over women sharing HRT products with others who are struggling to obtain medicines as a result of the supply problems. “While we appreciate the seriousness of the current situation and the frustrations women are experiencing, we urge them not to share HRT medication as this could lead to serious side-effects.”

The Guardian revealed on Monday that supply shortages have been so severe that some women have been forced to travel hundreds of miles in search of HRT products.

Health experts are increasingly concerned about the mounting impact of the issue on women’s physical and mental health.

“The impact the HRT shortage is having on so many women cannot and should not be underestimated,” said Dr Martin Kinsella, a hormone expert. “I’ve heard of women buying HRT on the black market and in doing so putting their own safety at risk, and some whose mental health as well as physical health has suffered hugely due to this shortage.”

Dee Murray, the CEO and founder of the Menopause Experts group, said: “The HRT shortage is causing stress and potential harm for women, with some pushed to take matters into their own hands and look for supplies online. This could have a devastating impact on their health, as HRT should only be prescribed by qualified healthcare practitioners who understand the patient’s history.”

Sajid Javid has been urged to change the law to let pharmacists alter prescriptions during medicine shortages. Claire Anderson, the president of the Royal Pharmaceutical Society, told the Guardian community pharmacists should be able to dispense substitute versions of medicines on prescription without having to contact the prescriber – typically a GP – every time. Currently, the law in England stipulates they must provide only the exact prescription.

Javid, the health secretary, has said he was “determined” to resolve the crisis and intends to use lessons learned during the Covid-19 vaccine rollout, as well as appointing an HRT supply tsar.