When direct effects of a drug cannot be measured, what is typically used instead?

When direct effects of a drug cannot be measured due to various factors such as time, feasibility, or ethical considerations, surrogate markers are typically used as a substitute. Surrogate markers are substitute endpoints that can serve as indirect measures of the drug's effect on a patient’s health outcomes. For example, if a medication is intended to reduce the risk of heart disease, a surrogate marker might be cholesterol levels rather than waiting to see if it actually reduces heart attacks over a longer period.

Using surrogate markers can allow researchers and healthcare professionals to assess the efficacy of a treatment more quickly and efficiently than waiting for the direct clinical outcomes, which may take years to observe. This is particularly valuable in drug development, where understanding a drug’s impact on a condition as early as possible can guide further research and clinical application.

Other options like diagnostic imaging, patient symptom diaries, and placebo responses have their own specific uses in monitoring treatment effects, but they serve different purposes than surrogate markers. Diagnostic imaging often illustrates structural changes, patient symptom diaries track subjective experiences, and placebo responses are used to gauge the psychological impact of treatment rather than provide a measure of the drug's biological effects.