SLC6A4 and depressive symptom measurement: However, currently there are no recommendations for drug dosing and selection considering polymorphisms in SLC6A4. It also seems noteworthy at this point, that besides effectiveness, SLC6A4 variants have been associated with antidepressant tolerability (39, 40) and even depression susceptibility with SLC6A4 variation as a potential disease modifying factor (41, 42).