No drug is free of risks, or the potential for causing harm. Every decision to take a drug needs to consider expected benefits and known risks. One of the ways we can reduce harms is by studying drug use rigorously. Only by understanding the “real world” effects of drugs can we understand the true risks (and benefits) and design strategies to reduce the risk of iatrogenic harm — that is, harms caused by the intervention itself. Adverse events related to drug treatments are common. Some lead to hospitalization. Studies suggest 28% of events are avoidable in the community setting, and 42% are avoidable in long-term care settings. That’s a tremendous amount of possible harm from something prescribed to help. A new study published this week shows that adverse drug events (ADEs) continue to cause significant problems, sending over a million Americans to the emergency room every year.