[One problem] is that industry-sponsored trials are more likely to show a beneficial effect than non-industry funded trials [261,536–540]… This bias can have paradoxical consequences. For example, Heres et al.  examined randomized trials that compared different antipsychotic medications. They found that olanzapine beat risperidone, risperidone beat quetiapine, and quetiapine beat olanzapine! The relative success of the drugs was directly related to who sponsored the trial. For example, if the manufacturers of risperidone sponsored the trial, then risperidone was more likely to appear more effective than the others.
The reference is Heres et al. (2006).