Thomas A. M. Kramer, MD


Medscape General Medicine. 2003;5(1) 

In This Article

Efficacy Vs Effectiveness

A major part of the drug development process is to weed out those compounds whose side effects overwhelm their therapeutic effects. This gets to the fundamental issue of efficacy vs effectiveness. A drug's efficacy is a measure of the ability of the drug to treat whatever condition it is indicated for. It is not a statement about the drug's tolerability or ease of use. Effectiveness is a measure of how well the drug works and encompasses all 3 of these issues. A drug may have very good efficacy but is so unpleasant to take that its actual utility is extremely limited. This would be determined in clinical trials, and the development of such a compound would cease.

For those drugs that do make it to market, there usually is a qualitative difference between side effects and therapeutic effects. The side effects of most compounds, psychiatric or otherwise, are transient. A drug company is much more likely to market a compound if whatever side effects it has go away in a few weeks. All of us who prescribe medications spend a great deal of our time with our patients reassuring them that the difficulties they may be having with their medication are temporary. This then begs the question: why are some drug effects short-lived and others long-lasting with chronic administration of the compound?


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