Millions of Americans may have the wrong prescriptions for aspirin, blood pressure and anti-cholesterol medications.

At issue, a recent study found, are the calculations used to determine the risk of stroke or heart attack. Stanford University researchers found that the calculations — known as pooled cohort equations — could be improved.

The equations help doctors decide whether to prescribe the medications, either alone or in combination, by estimating stroke and heart attack risk. Patients may be at risk from too much or too little medication if the equations used by doctors are based on outdated data, which has been a topic of debate in the medical community.

One of the main data sets used for the equations was derived from people who were 30 to 62 years old in 1948. Because much has changed with medical treatments, diets and the environment since then, researchers concluded the equations may be estimating people’s risk as too high. That could mean some patients today are getting too much medication.

Another factor is diversity: The old data may not have included enough African-Americans, meaning that calculations about their risk for heart attack and stroke may have been artificially low — giving them a false sense of security, the researchers noted.

The researchers have updated the equations with newer, more accurate data. The National Institutes of Health, which maintains the data, has approved the revisions.

The good news is that this vital information may finally be coming of age, in time to help you and your loved ones get the precise amount of medications you need.