According to an emerging body of research, the time of day you take a medication may influence how well it works, or how much it harms.

Tobias Eckle, from the University of Colorado School of Medicine, has been studying the relationship between circadian rhythms and drug efficacy for several years. Referred to as chronotherapy, this field of study looks to home in on how a human body responds to drugs at different times in our 24-hour circadian cycles.

Eckle said just four of the 50 most commonly used medicines in the United States have directions recommending they be taken at a specific time of the day. And there are two key reasons why doctors don't direct patients to take drugs at certain times.

"First, many physicians are not aware that some drugs work better during a specific time of the day," explained Eckle in an article for The Conversation. "And second, most drugs have not been studied for possible different effects during a 24-hour cycle. As such, patients are directed to take most drugs during the morning or evening primarily to ensure compliance."

Some studies over the past few years have started to point at certain specific relationships between drug efficacy and circadian cycles. A detailed 2019 study, for example, looked at how tumor growth can ebb and flow alongside circadian rhythms. The conclusion from that research was that certain breast cancer drugs should be administered in the morning to maximize efficacy.

Another compelling study investigated immune system activity and circadian cycles, wondering whether common non-steroidal anti-inflammatory drugs (NSAIDs) could negatively affect bone healing if taken at the wrong time. That research strikingly found that over-the-counter pain medicines may actually slow the rate of bone healing if taken late in the evening.