The survey, by YouGov for Lloydspharmacy, found that 81 per cent of people believed they had diagnosed a condition before consulting their GP or pharmacist. A total of 1,972 adults were interviewed.
Andy Murdock, pharmacy director of Lloydspharmacy, warned that misuse of the internet or other sources of health information could lead to dangerous outcomes.
'Of course it's good that people are taking more interest in their health and trying to understand what ails them,' he said.
'But people need to use the web as an additional source of information rather than as a substitute for timely advice and diagnosis by a clinician.
'While some websites, such as NHS Direct, contain well-researched and reliable information, there are many that do not.'
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