The proposed ban of nitrous oxide could stop users seeking medical help in hospitals, health experts have warned.
In a letter to the government, seen by BBC Newsnight, 15 neurologists and related health experts say possession of the drug should not be criminalised.
Despite rising numbers of hospital patients suffering the effects of so-called laughing gas, they warn the ban could worsen the stigma around users.
The government has responded, saying it plans to go ahead with the ban.
Nitrous oxide is a colourless gas often sold in metal canisters. It is one of the most commonly used drugs by 16 to 24-year-olds,
Heavy use can lead to nerve-related symptoms – being unable to walk, falling over, or experiencing tingling or loss of sensation in the feet and hands. Some users have nerve-related bladder or bowel problems, erectile dysfunction or incontinence.
Supply of nitrous oxide for recreational use is currently banned – but possession is not.
And earlier this year, the government proposed an amendment to the law – which could come into force before the end of the year – meaning it would become illegal to possess the drug.
Writing to the minister for policing, Chris Philp, the 15 medical professionals say making possession of the drug illegal was “unlikely to translate to health benefits in our patients”.
That is despite leading medics telling Newsnight they have seen an increase of nitrous oxide patients.
The author of the letter, Dr Alastair Noyce, Professor of Neurology and Neuroepidemiology, said the ban risked creating “fear of a criminal record” among young users.
“People may delay coming to hospital at a time when their symptoms are treatable,” he said. “The net effect of that may be that they develop long-term harm damages.”
He said there was “very little evidence that the criminalisation will lead to reductions in neurological harm and will impact people’s opportunities who are not in education and employment”.
The letter urged the government to fund a national education campaign in schools and through the media “to ensure the public understand the risks posed by nitrous oxide misuse”.
Under the proposals, those found in possession of the drug could face up to two years in prison, an unlimited fine, or both. The government has launched consultations of the plan, both with experts and the public.
Experts have previously said a ban on laughing gas will not stop people using it. The Drug Science scientific charity said a blanket ban was “completely disproportionate” and “would likely deliver more harm than good”.
However, Mohammad Ashfaq, who runs Kick It, a grassroots organisation in Birmingham, said the proposed ban would help stop misuse of the drug. “At the moment, it is very difficult for the police to completely eradicate,” he said. “Communities are getting frustrated. The law will make a difference. It would be a lot clearer.”
BBC Newsnight also spoke with Katherine Bramwell, from South Wirral, who said she didn’t know anything about nitrous oxide until her son got addicted. She says he found it hard to get off the substance due to the psychological dependence.
“When you’re the one going to pick your son off from somewhere and finding him just basically lay there – can’t walk, can’t speak. You know, you’re waiting for a call to tell you that your son is dead.”
In a statement to Newsnight, the government said it would proceed with the nitrous oxide ban. It said it had set out a “clear strategy” in its anti-social behaviour action plan “for the police to deal with the misuse of this substance”.