5-HTP(5-Hydoxytryptophan) is the immediate natural precursor for serotonin, which is the mood elevating neurotransmitter in the brain. Supplementation may help to increase brain serotonin levels which can have a beneficial effect on a number of issues including depression, sleep problems, and carbohydrate cravings. SSRI (Selective Serotonin Reuptake Inhibitors) like Prozac and Zoloft work by keeping serotonin around longer than would be normal. They do nothing to address the potential deficiency of serotonin production. My suggestion is if you suffer from depression you should try supplementing with 5-HTP. 5-HTP Synergy also contains vitamin B6 which is the vital B vitamin used in the production of serotonin.