Thirty-four RCTs (n=3,922) were included.
Over half of the studies reported enrolment rates: the median was 76% (range: 30 to 100) of eligible participants . Many studies failed to specify the primary outcome or report a power calculation and simply reported a range of outcomes. Many had small sample sizes. Blinding of the participants was not possible in most studies and it was generally unclear whether the outcome assessment was blinded. The antidepressant studies tended to have larger samples, placebo control and pre-specified primary outcomes but a shorter duration of follow-up.
There was marked heterogeneity between studies with respect to disorders, disease definitions, interventions, outcomes, duration of follow-up and the reporting of statistical data; this made it difficult to compare the findings of the studies.
Somatisation disorder or lower threshold variants (23 RCTs, n=3,298): the following interventions had positive findings (in one or more domains) measured by one or more RCTs:
CBT - improvement, most frequently reported in symptomatic domain, in 5 out of 7 RCTs (374 out of 564 participants);
antidepressants - symptomatic and psychological improvement in 3 out of 4 RCTs (522 out of 634 participants);
psychiatric consultation letter - functional improvement in 3 out of 4 RCTs (240 out of 278 participants);
PCP training - symptomatic improvement in one out of 3 RCTs (127 out of 1,089 participants);
a multicomponent nurse-administered intervention including CBT and antidepressants as indicated - psychological improvement in one RCT (n=200);
non-CBT psychotherapy - functional and psychological improvement in one out of 2 RCTs (98 out of 168 participants).
Two RCTs were negative, one of aerobic exercise (n=228) and one of disclosure through writing (n=137).
Hypochondriasis (5 RCTs, n=365): all 4 studies of CBT (n=345) had positive findings, as did a pilot study of explanatory therapy (n=20). The reported benefits were mainly in the psychological domain.
Body dysmorphic disorder (3 RCTs, n=140): CBT had positive findings in functional and/or psychological domains in 2 RCTs (n=73), as did fluoxetine in one RCT (n=67).
Conversion disorder (3 RCTs, n=119): the results of 2 RCTs using hypnosis and one using paradoxical intention were inconclusive.