In medicine, efficacy is the capacity for beneficial change (or therapeutic effect ) of a given intervention (for example a drug, medical device , surgical procedure , or a public health intervention). [ citation needed ] Establishment of the efficacy of an intervention is often done relative to other available interventions, with which it will have been compared. [ citation needed ] Specifically, efficacy refers to "whether a drug demonstrates a health benefit over a placebo or other intervention when tested in an ideal situation, such as a tightly controlled clinical trial."  These studies focus to a primary parameter to be shown statistically different changes between placebo and intervention groups. Comparisons of this type are called in 'explanatory' randomized controlled trials , whereas 'pragmatic' trials are used to establish the effectiveness of an intervention regarding also non-specific parameters. [ citation needed ]
These broad fields of endeavour encompass a wide variety of activities, such as developing systems of primary health care that reach the whole population of Member countries; promoting the health of mothers and children; combating malnutrition; controlling malaria and other communicable diseases including tuberculosis and leprosy; coordinating the global strategy for the prevention and control of AIDS; having achieved the eradication of smallpox, promoting mass immunization against a number of other preventable diseases; improving mental health; providing safe water supplies; and training health personnel of all categories.
Results Thirty-six trials were eligible, including 6778 participants (3484 [%] female; mean [SD] age,  years); 17 studies for DD, 10 for AD, 8 for OCD, and 1 for PTSD. Analysis showed that SSRIs and SNRIs were significantly more beneficial compared with placebo, yielding a small effect size ( g = ; 95% CI, -; P < .001). Anxiety disorder ( g = ; 95% CI, -; P < .001) showed significantly larger between-group effect sizes than DD ( g = ; 95% CI, -; P < .001). This difference was driven primarily by the placebo response: patients with DD exhibited significantly larger placebo responses ( g = ; 95% CI, -; P < .001) compared with those with AD ( g = ; 95% CI, -; P < .001). The SSRIs produced a relatively large effect size for ADs ( g = ; 95% CI, -; P < .001). Compared with participants receiving placebo, patients receiving an antidepressant reported significantly more treatment-emergent adverse events (RR, ; 95% CI, -; P = .01 or RR, ; 95% CI, -; P < .001, depending on the reporting method), severe adverse events (RR, ; 95% CI, -; P < .001), and study discontinuation due to adverse events (RR, ; 95% CI, -; P < .001).