In the United Kingdom, preparations for an experiment involving puberty blockers have been suspended following warnings from health authorities about possible “long-term biological harm” to children. This was reported by The Times, citing the country’s Department of Health and Social Care and a letter from the Medicines and Healthcare products Regulatory Agency (MHRA).

According to the newspaper, the trial planned by King’s College London was expected to include up to 250 volunteers aged 10 and older. The study proposed administering the drug to participants for two years, followed by monitoring until early adulthood. Researchers intended to assess brain development, quality of life, and participants’ physical and mental health compared with those who did not receive the medication. The project could have become the largest clinical trial of puberty blockers to date.

The UK Department of Health and Social Care stated that preparations for the trial have been paused. The study will only be allowed to proceed if expert scientific and clinical evidence confirms both its safety and necessity.

The newspaper also reported that the MHRA had written to King Charles III proposing that the minimum age of participants be set at no younger than 14 years. The agency’s letter warned of a high likelihood of fertility loss and irreversible bone damage among participants.

In March 2024, the UK’s National Health Service (NHS) announced it would stop using puberty blockers to treat gender dysphoria in children and young people. Officials explained that the drugs suppress the release of follicle-stimulating and luteinizing hormones from the pituitary gland, thereby delaying puberty and the development of secondary sexual characteristics.

In December 2024, the country’s health authorities also announced plans to permanently ban the sale and prescription of such medications for the treatment of gender dysphoria in individuals under the age of 18.