Today we released a new refine option in Trip, one for Controlled Trials (mainly RCTs).
After help with filters from Julie Glanville we have grabbed trials from PubMed and Mendeley and this has resulted in approximately 500,000 trials being added to Trip (too see the filter used, click here). Give the nature of filters used to highlight controlled trials there is a compromise between sensitivity and specificity. Over the next few months we'll work to improve the quality and also the quantity of trials.
In testing, I've used the feature extensively and it's worked really well. It really is a powerful addition to Trip. To use it yourself, simply go to Trip and search as you would normally and simply press the 'Controlled Trials' link/button in the refine area on the right hand side of the search results.