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People with chronic pain are being given antidepressants with very little scientific proof the medication helps, a major reviewhas found.

In studies, with nearly 30,000 patients, there was "moderate" evidence for only one drug, duloxetine, and just for short-term pain relief.

And there was a "shocking" lack of long-term data, even though the pills are usually prescribed for many months.

But patients are advised to stay on medication if it works for them.

They must not suddenly stop taking tablets without talking it over with a doctor, experts say.

NHS guidelines say:

• Antidepressants can be used for some chronic-pain conditions, including nerve pain and fibromyalgia
• Strong opioid painkillers, which can be addictive, are not recommended, nor are simple painkillers such as paracetamol and ibuprofen
• Exercise programmes and physical activity may help and some people might want to try psychological therapies such as cognitive behaviour therapy (CBT)

Chronic pain, lasting for more than three months, is extremely common - a BBC News survey suggests one out of every four of people in the UK is living with it.

There can be no obvious cause - or it might be linked to other health conditions, such as arthritis.

Experts say brain systems for mood and pain overlap considerably, which is why it has been suggested antidepressants may help. Hundreds of thousands of patients with chronic pain in the UK are thought to be on them.

• Chronic pain 'like walking into a burning hot oven'

The Cochrane review, led by scientists from several UK universities, including Southampton and Newcastle, examined 176 trials. But most looked at patients' experience over a couple of months only.

Among the drugs studied - which included Prozac and a cheap antidepressant called amitriptyline - only one, called duloxetine, showed any evidence for pain relief.

None of the trials gathered long-term safety and effectiveness data, which the researchers say is shocking and needs remedying to guide patients and doctors.

Prof Tamar Pincus said: "It's really shocking that we don't have any evidence for long-term use of even duloxetine.

"This is a global public-health concern. Chronic pain is a problem for millions who are prescribed antidepressants without sufficient scientific proof they help, nor an understanding of the long-term impact on health.

"But it does not mean that people should stop taking prescribed medication without consulting their GP."

Clinical lead for National Institute for Health and Care Excellence (NICE) chronic-pain guidelines Dr Cathy Stannard said: "This well conducted review adds to the substantial evidence we now have that shows that the use of medicines to treat long-term pain is disappointing."

But it could be difficult to translate results from clinical trials to real life.

"It's equally important to emphasise the many social and psychological influences on the pain experience," Dr Stannard said.

"Existing services, usually outside healthcare, including support with mobility, debt management, trauma, and social isolation, can be helpful for people living with pain - and identifying what matters most to people and signposting to appropriate local support is a promising way forward."

When coming off antidepressants, the medication should be slowly reduced over weeks to prevent withdrawal symptoms, says the NHS.