Which of the following describes an unfavorable response to treatment?

The term "iatrogenic" specifically refers to health complications or adverse effects that result as a consequence of medical treatment or intervention. This encompasses any undesirable outcomes that arise from a physician's actions, such as infections from surgery or negative side effects from prescribed medications. The essential characteristic of an iatrogenic condition is that it is a direct result of medical care, thereby aligning perfectly with the concept of an unfavorable response to treatment.

In contrast, the other options do not relate to adverse effects that arise from medical treatment. "Malady" is a general term for an illness or disease but does not imply that the illness is caused by medical intervention. "Prophylactic" refers to measures taken to prevent disease or health issues and does not imply any negative outcome. Similarly, "preventative" is associated with actions that seek to avert health problems and, like prophylactic, does not denote an unfavorable response. Thus, "iatrogenic" is the only term that directly addresses the concept of negative reactions stemming from medical treatment.