As many as one-third of customers in a 23andMe survey reported some sort of side effect from prescription or over-the-counter medication, according to data compiled by our researchers. The results confirm that people often experience unintended effects from medication. Most of the time those effects are minor, but many people reported side effects serious enough to either stop taking a drug, or prompt them to seek medical attention.According to a more than decade old study, “adverse drug reactions” (also referred to as “ADRs”) are one of the leading causes of death in the U.S. Other studies cited by the FDA indicate that more than 6 percent of hospitalizations are due to adverse drug reactions.The survey done by 23andMe is part of ongoing research that looks at differences in how people react to medication. There are some caveats in the data and the accompanying graphic. For one we don’t lump the drugs into classes – antibiotics, opiates and NSAID, for example. In the case of sulfa drugs, we list Bactrim – a sulfa drug – on its own. In part it is because this reflects the actual responses filled in by customers. The survey included responses from 68,782 customers. Of those, more than 33 percent said they’d experienced side effects serious enough to either stop taking medication, or that the side effects sent them to the hospital. The most common reported side effects were rashes, hives, nausea, vomiting and pain. Also in the top ten were side effects such as difficulty breathing, depression and anxiety. Customers reported that penicillin, sulfa drugs and codeine were most frequently reported to cause those side effects, the survey showed.Understanding why we react differently to medication can help both patients and those prescribing medication to avoid those problems. Patient error, interactions with other drugs or supplements or allergic reactions are sometimes to blame, but genetics can also play a role.At this year’s American Society of Human Genetics meeting in Boston, a team of 23andMe scientists presented research showing a genetic association with opioid-induced vomiting.Unlike many other pharmacogenetic studies that focus on very small cohorts, this study included more than 2,400 individuals who reported that the opioid codeine triggered vomiting. The study had about 10,000 controls, or individuals who reported no problems taking the pain medication.Beyond the relative robustness of the study, the research is also significant in that it looked at the genetics behind moderate side effects to a prescription drug. Rarely done in pharmacogenetic studies, moderate side effects still play a huge role in the relative effectiveness of medication because they impact whether people actually use the drug as prescribed.