Most medications are prescribed with a “one-size-fits-all” formula. But this can lead to side effects and lack of effectiveness in some patients. Now, a new study found that matching the dosages of prescription drugs to suit an individual’s DNA can reduce side effects by 30%. The findings are another piece of evidence that honoring DNA, and treating patients as individuals, can boost health outcomes.

According to Study Finds, a clinical trial involving 7,000 people from seven European countries found that when the participants used their DNA medication pass to help doctors and pharmacists determine which medications and doses were the best for them, they experienced 30% fewer side effects compared to people who received standard doses of medication.

The study authors randomly placed the participants into a genotyping group and had their DNA mapped out. They focused on 12 specific genes and 50 types of genetic variants and how 39 drugs affected them. About three months into the trial, a nurse contacted each participant and asked about side effects such as diarrhea, anemia, nerve pain, and muscle pain. The drugs ranged across medical fields from oncology to psychiatry, says Study Finds.

The researchers discovered that the people who used their DNA medication passes, with information from their DNA mapping, not only experienced fewer side effects but were happier, perhaps because they felt more in control of their health.

“This is a large landmark randomized study which shows that pharmacogenomic testing using a comprehensive genotyping panel can prevent adverse drug reactions, an outcome measure which is clinically important to individual patient and to healthcare systems,” said Sir Munir Pirmohamed, one of the study authors in a press release from the University of Liverpool, which was the only U.K. site of the clinical trial. “A 30% reduction in adverse reactions with a single intervention is remarkable.”

The study, published in The Lancet, is the first to demonstrate the practical application of using a panel of genes to tailor drug prescriptions to the individual. Due to variations in our genetic information, patients can react differently to a specific drug. For example, some people process medications faster than others and need a higher dose to achieve the desired effects. Others are slower to process certain drugs which could lead to nasty side effects. By being more precise with medication and doses, doctors and pharmacists can achieve optimal results for the individual being treated. The DNA medication pass could make treatment more effective and safer for millions of patients, said the study authors.