Summary of Systematic Review.

Exposures investigated by lead author of study. An “X” indicates whether the agent was evaluated by a particular study. The last row indicates whether there was sufficient evidence to demonstrate the studies estimated heterogeneous effects. Drugs with an asterisk (*) next to their names identify those implicated by the meta-analysis. Plus signs (+) indicate exclusion from analysis due to incompatible definition of exposure and/or reference group. “Greater Than” symbols (>) and “Less Than” symbols () or protection (