Purpose: The pathogenesis of chronic fatigue syndrome or myalgic encephalomyelitis (CFS/ME) is complex and remains poorly understood. Evidence regarding the use of drug therapies in CFS/ME is currently limited and conflicting. The aim of this systematic review was to examine the existing evidence on the efficacy of drug therapies and determine whether any can be recommended for patients with CFS/ME.

Methods: MEDLINE, EMBASE, and PubMed databases were searched from the start of their records to March 2016 to identify relevant studies. Randomized controlled trials focusing solely on drug therapy to alleviate and/or eliminate chronic fatigue symptoms were included in the review. Any trials that considered graded exercise therapy, cognitive behavior therapy, adaptive pacing, or any other nonpharmaceutical treatment plans were excluded. The inclusion criteria were examined to ensure that study participants met specific CFS/ME diagnostic criteria. Study size, intervention, and end point outcome domains were summarized.

Findings: A total of 1039 studies were identified with the search terms; 26 studies met all the criteria and were considered suitable for review. Three different diagnostic criteria were identified: the Holmes criteria, International Consensus Criteria, and the Fukuda criteria. Primary outcomes were identified as fatigue, pain, mood, neurocognitive dysfunction and sleep quality, symptom severity, functional status, and well-being or overall health status. Twenty pharmaceutical classes were trialed. Ten medications were shown to be slightly to moderately effective in their respective study groups (P < 0.05).

Implications: These findings indicate that no universal pharmaceutical treatment can be recommended. The unknown etiology of CFS/ME, and complications arising from its heterogeneous nature, contributes to the lack of clear evidence for pharmaceutical interventions. However, patients report using a large number and variety of medications. This finding highlights the need for trials with clearly defined CFS/ME cohorts. Trials based on more specific criteria such as the International Consensus Criteria are recommended to identify specific subgroups of patients in whom treatments may be beneficial.