The present invention relates to combination therapies and pharmaceutical compositions comprising a combination of 5-hydroxytryptophan and a serotonin reuptake inhibitor. The present invention provides a pharmaceutical composition comprising (i) a serotonin reuptake inhibitor and (ii) 5-hydroxytrytophan. The present invention further provides a pharmaceutical composition comprising (i) 5-hydroxytryptophan in an amount ranging from about 1 mg to about 75 mg; and (ii) a serotonin reuptake inhibitor. The present invention also provides a pharmaceutical composition comprising (i) a subclinical dose of a serotonin reuptake inhibitor; and (ii) 5-hydroxytryptophan.