If your PubMed search turns up a clinical trial, you may see a box linking to systematic reviews which have cited that trial. Not every clinical trial or systematic review in PubMed is included (yet). For now the National Library of Medicine is working on getting each of the 31,000 plus systematic reviews included in PubMed Health linked to the trials they cited.
From the PubMed Health website: “PubMed Health provides information for consumers and clinicians on prevention and treatment of diseases and conditions.
PubMed Health specializes in reviews of clinical effectiveness research, with easy-to-read summaries for consumers as well as full technical reports. Clinical effectiveness research finds answers to the question “What works?” in medical and health care.”
For more information about this new feature, see http://www.nlm.nih.gov/pubs/techbull/jf14/brief/jf14_pm_health_blog_trials_sys_reviews.html