The research pooled results of studies, some unpublished, submitted to the US Food and Drug Administration (FDA) into fluoxetine (Prozac), venlafaxine (Efexor), nefazodone (Serzone) and paroxetine (Seroxat).
Known as selective serotonin re-uptake inhibitors (SSRIs), these drugs are widely prescribed for treatment of depression.
The study, conducted by researchers at the University of Hull, looked at the overall improvement in Hamilton Rating Scale of Depression (HRSD) scores from 47 clinical trials.
Results showed that although the mean improvement in patients’ scores of 1.8 was statistically significant, it was below the score of three suggested by NICE as being clinically significant.
Only when trials involved the most depressed patients did they reach clinical significance, the report added.
The study authors said: ‘This pattern is due to a decrease in the response to placebo rather than an increase in the response to medication.’
PLoS Medicine (2008) 5: 260-268