The hormone melatonin is being handed out too readily to children who are struggling to sleep, despite the fact little is known about the long-term risks of taking it, experts have warned.

Melatonin, a hormone the body produces naturally in reaction to darkness that helps prepare us for sleep, has been authorised for use among the over-55s, and has been hailed as a less-addictive alternative to drug treatments for insomnia.

But after a surge in the number of children under 14 being admitted to hospital with sleep disorders over the last decade, specialists are concerned that it is being given to children ”off label” – with little knowledge of the long-term safety or side-effects. They fear that it may be being overprescribed by paediatricians and has become a fashionable treatment for parents who want “perfect” children.

While NHS data on prescriptions does not give figures for children specifically, there has been a tenfold increase in the number of melatonin prescriptions among the under-55s in general over the last 10 years. Dr Neil Stanley, an independent sleep expert and former director of sleep research at the University of Surrey, said that overuse of the treatment for children had been brought to his attention by the GPs and nurses he lectures, who dispense it after it is prescribed by paediatricians.

“Unless a child has a diagnosed condition such as autism that has been scientifically proven to be helped by melatonin, there is no medical rationale for a child to be given it,” he said. “Most paediatricians know little about sleep or melatonin. For non-autistic children it is a fashionable treatment for parents wanting ‘perfect’ children.”

When given as a medicine, melatonin is usually made synthetically in a laboratory. The short-term side effects are thought to be minimal, but it can cause headaches, nausea, dizziness and drowsiness. However, in the long term there are ongoing concerns based on studies in animals showing melatonin can affect puberty-related hormones.

Vicki Dawson, founder of the NHS Doncaster-funded the Children’s Sleep Charity, the only free specialist service that provides support to families for children’s sleep, said lots of children are being prescribed melatonin “often because there is no behavioural support for sleep available”.

She added: “One of our aims is to lower melatonin prescription levels. For example, in Doncaster children are now not prescribed melatonin until they have been through behavioural approaches to sleep.”

Dawson said: “Sometimes there is a place for it [melatonin]. We work closely with paediatricians and there are times when we will say we think it is helpful but only for short periods of time. My concern is some children are on it as a long-term solution. I have worked with kids on it six or seven years.”

Guidance from the National Institute for Health and Clinical Excellence (Nice) about using melatonin says it appears relatively safe in the short and medium term (using it for up to 18 months). But the safety beyond that and in the longer term is unclear.

Mandy Gurney, health visitor and founder of the Millpond Sleep Clinic, said she had also heard from a child who was on it for years. “We were commissioned in Wales to run workshops for community staff because of concerns about high prescription levels in children. The manager in charge was concerned ... The levels of prescription dropped after we left.”

She added: “It should be targeted to children with known conditions that can lead to low melatonin levels ... and not just dished out because there is no time to do things like behavioural programmes to improve sleep, which are known to be more effective.”

Dr Liz Bragg of the Royal College of Paediatrics and Child Health, said: “I don’t want to criticise fellow practitioners by saying it is being overprescribed, but I wouldn’t like to prescribe it unless work has been done to make sure the right sleep advice has been given and ... the right bedtime routine to wind down to sleep is put in place.”

Prof Paul Gringras, who leads the sleep medicine unit at Evelina London Children’s hospital, similarly expressed more caution about saying it was overprescribed. He added that it should not be given to children when no behavioural techniques had been tried.

“I wouldn’t prescribe melatonin if I didn’t know good bedtime routines were in place,” he said. “I would agree you need to be careful as seeing it as a quick fix, but when appropriately prescribed for those with autism and other problems melatonin can be very effective for the children and their families.”

He added: “Children with autism and other developmental problems often don’t make enough melatonin at night, or produce it too late ... that’s why it works well for those groups.”

Gringras warned against parents giving children melatonin without a prescription. The Guardian found posts in parenting forums with people asking where to get it online. One parent on Mumsnet wrote: “You should not be able to buy it in the UK, however, if you search the internet (or eBay) you will probably manage to find it. It may be called melatonin amongst other things.”

Dawson said: “There is a lot of misunderstanding about it. Parents are aware you can get it in the US in supermarkets. I’ve had parents say it is a natural remedy, but it’s not. There needs to be more awareness about what it actually is and possible long-term side effects.”

A Royal Pharmaceutical Society spokesperson, Lesley McArthur, said: “I’d be concerned about people buying melatonin online. It’s a prescription-only medicine and you can’t be certain that what you are buying is the real thing ... Parents should try small lifestyle changes first before reaching for medication.”

McArthur added: “The use of melatonin has increased. Starting a child on melatonin should ideally be done in conjunction with a paediatric sleep specialist. It is essential that each child’s case is reviewed as if the melatonin has had no effect the sleep problem is probably not responsive to the treatment and it should be stopped.”