More recent research shows that taking aspirin is only useful to reduce the incidence of a second heart attack or prevent stroke. It has absolutely no added benefit for those who have never had a heart attack. Considering that long-term use of aspirin can have negative effects on digestion, it’s best not to take it unless you’ve already had a heart attack.
Besides extending scientific results to other populations (assuming studies in men apply to women) we often extrapolate the data to other situations (results in one disease apply to other diseases). This is what doctors often do when they try what is called “off label use”. It is actually a continuation of the research and doctors are aware of this. When a drug has proved useful for one health problem it is often prescribed for a related health problem. This approach has been proven helpful in some cases, for instance using Depakote (a drug for seizures) for people with bipolar disorder.
However, there are certain drugs that are used for many unrelated health issues. I think this is partly because both the doctor and the patient want to feel that something is being done when no effective treatment is available. This is especially true if the drug is generally well tolerated. An example is the many uses of antidepressants. Sometimes they are indeed helpful (irritable bowel syndrome), and sometimes they are not (peripheral neuropathy).
It’s also important to remember that not everyone in a clinical study, even if they are all “men in their 50’s who had a previous heart attack”, responds the same. No drug has ever worked for 100% of the subjects tested. When you hear some new scientific fact ask about the conditions of the study. If something proves preventative for people who’ve already had a heart attack, it may not be helpful for people who never had and are unlikely to ever have a heart attack. because it’s not in their constitutional makeup.
Both doctors and patients need to remember that clinical studies are a matter of statistics and that all patients are unique individuals. When prescribing and taking drugs one should always proceed with caution.