According to a survey by women’s health brand Balance Active, 50% of women diagnose themselves online and take medication before consulting a doctor.
The survey also says that one in four women have taken the wrong medication after turning to the Internet instead of talking to a doctor.
The survey of 1,000 women found one in ten have suffered bad side effects because of self-diagnosis online.
Headaches, depression and sleep problems were most likely to cause women to diagnose themselves; the most common false alarm was breast cancer.
A third said they had spent at least two weeks with a medical problem before speaking to a doctor.
The most popular reason for self-diagnosis was because women didn't want to make "a fuss" while a third say they can gain answers "more quickly online."
Penny McCormick of Balance Active said: "The web gives us a wealth of information that can be useful in reducing our worries until we’re able to gain proper advice from a medical authority. But the results show how easy it is to make mistakes when diagnosing ourselves. Misdiagnosis can be serious, as it may delay treatment for the real problem that needs attention."