It can be easier than you think to become a drug addict, as Cathryn Kemp discovered the hard way.
Asked to conjure up an image of a drug addict, most people would picture a stereotypical 'junkie' - unkempt, down and out, with needle marks puncturing their arms.
Kemp couldn't be further from that. At 41, she's smart, attractive, middle-class and has travelled the world as a successful travel writer.
Until quite recently though, Kemp was within months of losing her life to an all-consuming drug addiction.
Yet throughout her two-and-a-half-year nightmare, Kemp wouldn't have had a clue how to 'score' illegal drugs from a backstreet dealer.
She was addicted to prescription painkillers - entirely legal and prescribed by her GP to help her deal with chronic pain.
Kemp describes her experiences in her new book, Painkiller Addict, which is an honest and eye-opening account of a problem that is affecting increasing numbers of people.
According to a recent report by the Parliamentary Drugs Misuse Group, an estimated 1.5 million people in the UK are addicted to benzodiazepine drugs (sleeping pills and tranquillisers) alone, and the number of prescriptions for addictive drugs has risen dramatically in recent years.
According to a report by the National Treatment Agency for Substance Misuse last year, prescriptions of highly-addictive painkillers increased six-fold over the past two decades.
"Strong painkillers saved my life, but then they almost killed me," says Kemp. "And the way it happened to me, it could happen to anyone."
Kemp was first prescribed fentanyl, a very strong painkiller, after being discharged from hospital in 2007, following years of treatment for chronic and agonising pancreatitis.
Fentanyl is significantly stronger than heroin and after initially taking the recommended dose, Kemp increased the number of fentanyl lozenges she took when her relationship broke down.
She says that while she knew the drug wasn't the answer to what she was going through emotionally, she took the extra lozenges to help calm her down, as well as to numb the physical pain from the pancreatitis.
"It didn't occur to me that it could be the start of something I couldn't control," she explains.
"My doctor prescribed the drugs for me, so I assumed I was safe using them, even if I was pushing the limits by taking an extra few."
However, the extra few soon became a multitude. The more she took, the more her body got used to them, so she needed even higher amounts to combat her pain.
Within two years, Kemp was taking more than 10 times the NHS maximum dose, all on prescription, and the addiction was having a huge impact.
She became paranoid, thought demons were after her, and would hear whispering. Kemp even tried to kill herself by throwing herself out of a hospital window.
"I was completely bonkers," she admits.
Her desperation for the drugs meant she lied to her family and friends. She'd shake and suffer other terrible physical symptoms if she didn't get her regular fix.
Her GP realised fairly quickly that Kemp was addicted, and tried to make her face it and reduce her dose.
"He wanted me to realise what I was doing, but I absolutely refused to see I was addicted," Kemp recalls, explaining that she used her history of chronic physical pain to justify her need for the drugs.
"I had massive pain issues, and at the time I felt the drugs gave me quality of life and I played on that.
"These strong opiates are highly addictive - lots of us are only one car accident or one case of back pain away from really strong medication."
Kemp found out the hard way, just how addictive prescription painkillers can be, and now feels strongly that they are being over-prescribed.
Indeed, recent figures reveal that GPs handed out 1.38 billion prescriptions for opioid analgesics (highly-addictive painkillers) in the UK in 2009, compared with just 228 million in 1991.
Kemp was unable to work and often bedridden as a result of her problems, but the turning point only came when her GP stopped prescribing her the drugs.
She was forced to borrow money from her parents and sell her cottage to help pay for rehab. Detoxing was harrowing but, thankfully, successful.
"When I got into rehab they said I only had three months left to live, if I carried on taking the drugs," she says.
Her hair was falling out, and she such bad muscle wastage that she couldn't even sit up.
"The fentanyl unleashed a monster within me that almost destroyed my life, and that's the illness of addiction," she says.
"It's a chronic mental illness with the accompanying physical dependency, but we still treat addiction as a kind of moral failing and it's very different to that."
Kemp says the fear of confronting her pain was what kept her addicted for so long, and explains: "I'm not proud of being a drug addict, but I'm proud I found the courage to come off them and I'm proud I stuck with the withdrawal.
"A huge part of the battle is admitting it, and getting help."
She still has constant pain from her pancreatitis, but has learned to deal with it in other ways and now takes no drugs at all.
"I have pain all the time, but the fear of painkillers is now a lot stronger than the fear of the pain."
Consultant addiction psychiatrist Dr Tim Williams warns that while the route to taking drugs may be different - some users, like Kemp, may be prescribed them, while others may buy heroin on the streets - the end result is the same.
"They become dependent both physically and psychologically. But having said that, a lot of people can use opioids in a dependent way and suddenly stop them without too much problem."
He explains that while it's not clear why some people become addicted and others don't, genetics may make people more vulnerable to addiction, and environmental factors, particularly stress during childhood, can also play a part.
He agrees that dealing with addiction, where a person started taking a drug for a legitimate reason, such as prescribed pain relief, can be tough.
"It can be an incredibly difficult scenario to manage because there's a legitimate reason why they started taking the drug," he says.
"But the drug-seeking behaviour takes over. Pain is a very subjective experience.
"Physical and emotional pain can become mixed. But it's extremely difficult when someone's got a very painful physical condition as well.
"It can be a very simple solution to have a tablet to numb it, but it doesn't solve the problem in the long-term."