When serotonin levels are low, many psychological problems can develop including serious depression.
Serotonin levels are not routinely checked before prescribing serotonin-elevating agents. Since blood serotonin levels correlate poorly with brain levels, a therapeutic trial with agents that are known to raise levels is a reasonable and cost-effective approach.
One must be cautious not to combine too many SRIs (Serotonin Reuptake Inhibitors) such as Prozac, Paxil, Zoloft, Effexor, St. John's Wort (hypericum), and 5HTP to avoid the medical condition known as serotonin syndrome. Here the brain has too much serotonin (the opposite of what happens in depression) and this may result in symptoms such as sweating, agitation, confusion, lethargy, tremor, and muscle jerks. If such symptoms occur, consult your doctor immediately.