A year after dropping out of university, Liu Pinyi manages a smile as she makes her way to a special medical centre for internet junkies in Beijing. At the height of her obsession, the former telecommunications student once spent an entire week playing online games in an internet cafe. 'The real world meant nothing to me when I was fully involved with online games. I lost track of time, space, hunger, pain, everything. But after I finished, I immediately dropped into an abyss and didn't want to communicate with anybody,' she said yesterday. Ms Liu, 19, is not an isolated case, nor even one of the more extreme examples among the enormous number of mainland internet addicts, most of whom are teenagers. An estimate based on surveys puts the number of teenage internet addicts at 4.4 million - or 15 per cent of teenage internet users. One of the more harrowing cases of net dependency is that of 15-year-old Cui, from Henan province . Born into a wealthy family but shipped off to nurseries and boarding schools since the age of one, Cui rarely received attention from his busy, stern father. Obsessed with computer games and eventually turning to theft to pay for his internet time, Cui was soon kicked out of school. The teenager lost touch with his family and joined a gang that harassed elderly homeowners on behalf of property developers. Like many of the people at the medical centre, which can accommodate 14 people at a time for stays of between 10 and 15 days at a cost of 400 yuan a day, Cui was forced there by his parents. Tao Ran, director of the centre which is linked to the Beijing Military Hospital, said all the patients had psychological problems. They suffered from anxiety and stress. Half were depressed, while compulsive behaviour and communication difficulties were also common. Regardless of their similarities or differences, medical experts say one thing all internet addicts share with each other - and other addicts - is a chemical imbalance in the brain. An organic compound released when the mind is stimulated, 5-HT, transmits feelings of euphoria or depression throughout the body. When the compound is being secreted, it can trick the body into thinking it does not need sleep or food. And the body craves 5-HT, meaning people experience withdrawal symptoms - such as sweating, an increased heart rate, anxiety, headaches and sore muscles - if the level of release is too low or irregular. Physical dependency can be cured by injections, but the key problem is changing the underlying psychology. Ms Liu said she went online for satisfaction, when she was deeply unhappy about her life at university. 'All the values my parents taught me, which I strictly followed for 18 years, suddenly collapsed when I entered my campus, where I found students could easily cheat each other in order to achieve their objectives,' she said. Cui, who first used a computer 10 years ago, said he went online to escape a world where he was not able to find a purpose. Experts say the pressure of achievement-minded parents and China's skewed educational system, which stresses rote learning at the expense of developing imagination, are also to blame. 'Internet addiction is just a reflection of anxiety, an absence of a sense of security, and a loss of traditional values and beliefs in the rapidly developing Chinese society,' Dr Tao said. 'If the entire social sphere continues to push for material gains while marginalising a child's spiritual development, the centre's treatment will never be enough.' Ms Liu, who was admitted to the centre yesterday, says she is optimistic about the future. 'I came here to change my life ... and never make my parents sad again,' she said. 'I believe everyone here, including myself, will try to get our lives back.'