A ban on prescribing puberty blockers to children was motivated by the then UK health secretary’s personal view and not backed by evidence, the high court has heard.

The advocacy group TransActual and a young person who cannot be named are challenging the emergency order issued on 29 May that temporarily banned the drugs for young people with gender dysphoria in England, Scotland and Wales, which they say has had “a very real human cost” on more than 1,000 under-18s.

Representing the claimants at the high court on Friday, Jason Coppel KC said: “There is evidence of both self-harm and suicide attempts as a direct result of the legislation.”

Victoria Atkins, the health secretary at the time, changed regulations in the wake of the review by Dr Hilary Cass into gender medicine, which criticised the lack of evidence surrounding the benefits and the risks associated with puberty blockers but did not recommend a ban.

Coppel said Atkins had not identified the “serious danger to health” needed to justify emergency legislation, which bypasses the usual statutory duty to consult with a specialist committee of medical experts before a ban is brought in.

In written arguments, he said: “The evidence shows that the impetus and only disclosed rationale for the making of the order was the personal view of [Atkins] that the Cass report required immediate action.

“Officials were then tasked with working up arguments in favour of a banning order to fit that personal view. No clinical or other scientific advice was taken on whether the statutory criteria were, or were capable of being, satisfied. This was a wholly insufficient basis for invocation of the emergency process.”

The ban means that puberty blockers cannot be obtained from private prescribers and only from the NHS within a clinical trial, but Coppel said no trial had yet been established, despite Cass’s support for it.

He told the court that it was unprecedented for an emergency order to be issued to prevent new patients from being prescribed with an allegedly dangerous drug while existing patients continued to receive it, to prevent non-NHS use of a drug for particular patient groups while allowing continuing NHS use of the drug, and banning a drug when its use was consistent with international guidelines.

He said: “There must be a reliable body of evidence that a medicine presents a serious danger to health and not merely that it carries potential but unproven risks.”

Julian Milford KC, acting for the Department of Health and Social Care, said in written arguments that the emergency order was created because, despite a change in NHS England (NHSE) policy with respect to puberty blockers after the Cass review, it did not directly affect private prescribing domestically or by European Economic Area prescribers, which continued to issue them “through methods that fell alarmingly short of acceptable UK practice and were fundamentally unsafe”.

He added: “[The health secretary] reasonably took the view that it was essential to enact legislation with immediate effect to ban such prescribing, and restrict other inappropriate prescribing, to avoid serious danger to health.

“A precautionary approach was entirely appropriate where the safety of vulnerable children was in issue. Legislative action was supported and indeed encouraged by the review, NHSE, the medical regulators and the Royal College of GPs.”

He said Atkins’s decision that an emergency order was necessary was a “complex assessment, involving the application of clinical judgment, with which the court should be slow to intervene”.

Milford told the court that the unknown long-term effects of medicines upon children, including their brain health and sexual and gender identity, “entirely merited the characterisation of ‘serious danger to health’”.

He said TransActual had not been excluded from the consultation process as had been claimed because there was no consultation, just a “limited stakeholder exercise”. Even if consulted, he said, it “would not have led to a substantially different outcome”.

Judgment is expected at a later date. The Labour government has said it will seek to make the ban permanent, subject to the outcome of the case.