A 1998 study of 29,133 male smokers in Finland showed 32% less cases of prostate cancer and 40% less deaths from prostate cancer among men who took vitamin E to prevent lung cancer compared to men who took a placebo.
Research results on the efficacy of St. John's wort have been inconsistent, with some studies finding the herb to be as effective as selective serotonin reuptake inhibitors (SSRIs) and others finding it no more effective than a placebo.
The control group took a placebo, while the experimental subjects took the drug that was being tested.
Dry mouth, transient rise of serum alanine aminotransferase values and sleeping disorders have been reported more frequently than in patients receiving placebo.
Systematic review The review used an extensive search strategy for randomized double blind studies comparing antidepressants with placebo, or with other drug treatments.