Having a cocaine binge at the weekend followed by three or four diazepam to get to sleep on Sunday messes up the brain's chemistry, a consultant psychiatrist says.Many people who use drugs recreationally also take prescription medicines such as tranquillisers, sleeping pills and painkillers to deal with the effects of a weekend high and get back to work on Monday, new research reveals. An international survey carried out by the Guardian and Mixmag magazine found that about a third of the 7,700 people from the UK who revealed their illegal drug use also took prescription sleeping pills – 22.4% had taken benzodiazepines such as temazepam in the last year and 7.2% had taken the newer "z-drugs" – zopiclone and zolpidem. Those taking part in the survey were predominantly well-educated working people who felt they were in control of their lives. But Dr Richard Bowskill, consultant psychiatrist and medical director of the Priory rehabilitation centre in Brighton, said he saw the fallout years later from this pattern of illegal and prescription drug-taking among "highly functioning" clients. "People think they are being their own pharmacist. They have a major binge of cocaine over the weekend and three or four diazepam to get to sleep on Sunday night. They think they understand what it is doing to their body and they think they are in control, but their brain chemistry is getting messed up," he said. "They know the effects of the drug. It's often being used following cocaine to self-medicate for the downswing and it causes chaos. It's a really common scenario. Then they can't get to sleep on Monday and they take some more sleeping tablets." While recreational drug users think prescription medicines are safe, because GPs hand them out and the tablets are what they purport to be, benzodiazepines and opioid painkillers are highly addictive if taken regularly for any length of time. Anna, who had a high-pressured job requiring her to make frequent long-haul flights, was not a recreational drug taker but started taking zopiclone to help her sleep on the plane or when she arrived in a different time zone and needed to be fresh for work in the morning. "Your body gets accustomed to the drugs. I didn't really understand their addictive nature," she said. "They weren't having an effect so I was having to up the dosage." She ended up taking five tablets at a time, but they just made her more anxious, irritable and sleepless. "I lost a lot of friends." She talked of the societal "pressure to perform" and her regret that there was so little help. GPs did not want to know, she said. With the help of the Council for Information on Tranquillisers, Antidepressants and Painkillers (CITA), a support group, she had been switched to a different drug and was slowly cutting down. Against expectations, most people in the Guardian/Mixmag survey did not get their prescription drugs from the internet, but from their own GP or a friend who had been prescribed them. GPs were in a bind, said Dr Peter Swinyard, national chairman of the Family Doctor Association. When people arrived in the surgery complaining of pain or insomnia "we are predisposed to believe what people tell us", he said. "We always work from the premise that they are being honest with us." Nonetheless, a survey the association did last summer showed that 52% of GPs were worried about prescription drug abuse in their area. Eight out of 10 of the 197 GPs who responded to the survey said they were aware of prescribing to people who they thought were addicted. Half were aware of occasions when prescriptions had been sold on. "People tell us they lose their prescription or it got eaten by the dog. A lot of general practices have systems like a book at reception recording those who say they have lost their prescription," Swinyard said. But there are people who GPs would not characterise as liars or cheats. "There is the traditional little old lady who is taking her sleeping pill prescription and selling it down the pub. I'm sure there is a cohort of elderly people supplementing their pension by selling their prescription drugs," he said. Although the Guardian/Mixmag survey responders mostly said they used sleeping tablets for sleep and painkillers for pain, they had often tried them to get high – 57.8% in the case of the anti-hyperactivity drug Ritalin, nearly 40% in the case of the benzos and 28% who had taken opioid painkillers. In the US, prescription opioids have caused a huge problem since oxycodone – better known by its brand name OxyContin – was licensed for use outside cancer treatment in the mid-1990s. In 2008, 15,000 Americans died from overdosing on prescription opiates, according to the Centres for Disease Control (CDC), which is more than on heroin and cocaine combined. The opioid epidemic appears not to have hit the UK. "There has been a rise in oxycodone deaths, but it is pretty small," said James Bell, addiction consultant at the South London and Maudsley NHS trust. "I have been trying to look for evidence here and it is not a big problem." Demand was fuelled in the US by direct advertising to the public. In the UK this is not allowed and most people are registered with a single NHS GP so cannot shop around. The Guardian/Mixmag study, which was conducted by Global Drug Survey, shows that a quarter of responders had taken prescription opioid painkillers and 9% had taken other painkillers. More than three-quarters said they took them for pain relief, 24% said they took them to get to sleep and 18% said they took them for mood-changing purposes.