Use these pre-formulated search strategies (database-specific) to increase the sensitivity of a search for randomized controlled trials. to do so, just copy and paste the appropriate strategy into the database search box:
((randomized controlled trial[pt]) OR (controlled clinical trial[pt]) OR (randomized[tiab] OR randomised[tiab]) OR (placebo[tiab]) OR (drug therapy[sh]) OR (randomly[tiab]) OR (trial[tiab]) OR (groups[tiab])) NOT (animals[mh] NOT humans[mh])
Box 6.4.a, http://handbook-5-1.cochrane.org/
((randomized controlled trial or controlled clinical trial).pt. or randomized.ab. or randomised.ab. or placebo.ab. or drug therapy.fs. or randomly.ab. or trial.ab. or groups.ab.) not (exp animals/ not humans.sh.)
Box 6.4.c, http://handbook-5-1.cochrane.org/
crossover-procedure/ or double-blind procedure/ or randomized controlled trial/ or single-blind procedure/ or (random* or factorial* or crossover* or cross over* or placebo* or (doubl* adj blind*) or (singl* adj blind*) or assign* or allocat* or volunteer*).tw.
126.96.36.199. What is in The Cochrane Central Register of Controlled Trials (CENTRAL) from EMBASE? http://handbook-5-1.cochrane.org/
(NB: does not remove animal studies as the MEDLINE version does)
The Systematic Reviews wiki includes a list of other sites containing filters/hedges (both validated and unvalidated) as well as some specific ones for indigenous health in Canada, Canada and Low and Middle Income Countries (2012).