Benefits and harms of preventive health activities 

There is evidence that some preventive activities are not effective and may even be harmful. Determining whether a preventive activity is beneficial, harmful or of indeterminate effect (ie there is not enough evidence on which to base a decision) requires a consistent, unbiased, evidence-based approach. Screening of asymptomatic patients may lead to overdiagnosis, causing needless anxiety, appointments, tests, drugs and even operations, and may leave the patient less healthy. Therefore, it is crucial that evidence clearly demonstrates that the benefits outweigh those harms for each preventive activity.