The aim of this study is to investigate the efficacy of trazodone in the treatment of selective serotonin reuptake inhibitor(s) associated sexual dysfunction. The secondary domains assessed were the relationship between 5-HT2A polymorphism and treatment efficacy.

Inclusion criteria were:

1. 20-65 years of age,
2. receiving SSRI treatment for more than four weeks,
3. minimal dose of fluoxetine, paroxetine, and citalopram are 20 mg/d, minimal dose of fluvoxamine and sertraline are 50 mg/d, and minimal dose of escitalopram is 10mg/d,
4. developing sexual dysfunction based on the definition of Arizona Sexual Experience-Chinese Version.

Exclusion criteria were:

1. receiving other antidepressant agents,
2. receiving antipsychotics,
3. having a currently unstable medical condition such as unstable angina or uncontrolled diabetes,
4. having any serious medical condition that affects sexual functioning such as epilepsy, serious head injury, brain tumor, HIV infection, Parkinson's disease, dementia, multiple sclerosis, or other neurological disorder,
5. being pregnant or planning to become pregnant during the study period,
6. experiencing psychotic symptoms,
7. being comorbidity with substance abuse, (8) developing sexual dysfunction before receiving SSRIs treatment.