I have a feeling that with the advent of generic Prozac (fluoxetine -- available for $4 copay at Walmart) that the kickback is rather small, not that it ever existed.
"Compared to placebo, treatment with SAMe was associated with an improvement of approximately 6 points in the score of the Hamilton Rating Scale for Depression measured at 3 weeks (95 percent CI [2.2, 9.0]). This degree of improvement is statistically as well as clinically significant and is equivalent to a partial response to treatment".
http://www.ahrq.gov/clinic/epcsums/samesum.htm