Search Strategy
Four online databases were comprehensively searched, including: Embase, MEDLINE (via PubMed), Web of Science and Cochrane. Additionally, clinicaltrials.gov was searched to account for any possible on-going trials or unpublished data. There were no restrictions to language or publication period in any of these searches. The search strategy varied between different databases, however an example of such a search strategy as used in MEDLINE with medical subject headings (MesH) is presented in Table 1.