We searched on PubMed (1966 to 1 February 2015), EMBASE (1980 to 1 February 2015) and the Cochrane Central Register of Controlled Trials (the Cochrane Library 2015). 
PubMed
We searched on PubMed (1966 to 1 February 2015), EMBASE (1980 to 1 February 2015) and the Cochrane Central Register of Controlled Trials (the Cochrane Library 2015). 
EMBASE
We searched on PubMed (1966 to 1 February 2015), EMBASE (1980 to 1 February 2015) and the Cochrane Central Register of Controlled Trials (the Cochrane Library 2015). 
Cochrane Central Register of Controlled Trials
We searched on PubMed (1966 to 1 February 2015), EMBASE (1980 to 1 February 2015) and the Cochrane Central Register of Controlled Trials (the Cochrane Library 2015). 
The Cochrane Library