After further removing duplicates (N = 16), excluding review articles (N = 5), studies not measuring SERT occupancy by antidepressants (N = 23), studies administering the drug intravenously (N = 4), an animal study (N = 1), studies using a between-subjects design (N = 4), studies using the non-selective ligands [11C](+)-McN or [123I]-ß-CIT (N = 20), studies of drugs not approved for use in depression or that have been withdrawn (N = 8), and studies not providing occupancy expressed as a mean (N = 3), a total of 16 articles (reporting on 17 unique studies) were included [17–19, 28–40]. This evidence concerns the gene SLC6A4 and major depressive disorder.