A prospective longitudinal cohort study that will assess the effect of a Personalized Medicine (PM) clinic recommendations on pharmacogenetic variation and/or interacting drugs on plasma drug exposure, effectiveness or toxicity of commonly used antidepressant, pain, and antiemetic medications in cancer patients. Such recommendations will entail genotype-guided treatment suggestions while also considering potential DDI, and will be provided to patients during their clinic visit, and referring physicians thereafter. Drug concentration and therapeutic effectiveness will be assessed before (baseline) and 6 months after recommendations have been provided. To assess effectiveness, patient-reported outcomes will be evaluated using validated scales for symptoms of depression, pain and chemotherapy-induced nausea/ vomiting

The investigators hypothesize that the pharmacogenetic variation and DDI, if applicable, determine steady state drug concentration and therapeutic response or toxicity of the investigated antidepressant, pain or antiemetic treatments at baseline, while there is a clinically significant reduction or absence of the effect 6 months after the PM clinic recommendations to referring physicians and patients.

This prospective longitudinal study will consist of three cohorts of adult cancer patients routinely referred to the PM clinic for genotype-guided chemotherapy including 5-FU or tamoxifen that are also taking antidepressant, analgesic and/or antiemetic medications.

Patients will be assigned to one or more cohorts, as appropriate, at the screening visit: Cohort 1 (n=200) if prescribed antidepressants including the selective serotonin reuptake inhibitors (SSRI) citalopram or escitalopram, or the selective norepinephrine reuptake inhibitors (SNRI) venlafaxine or desvenlafaxine; Cohort 2 (n=200) if prescribed opioid pain medications including codeine, oxycodone, hydrocodone, or tramadol; and/or Cohort 3 (N=200) if prescribed the antiemetic agent ondansetron.

Each patient will participate in a PM clinic screening visit. Eligible patients will attend three subsequent study visits at 0.5, 4 (virtual), and 7 months after screening. At each PM clinic visit, clinical information and a venous blood sample will be collected. Patients will also complete the ESAS survey and validated scores/ surveys to evaluate treatment effectiveness.

Inclusion Criteria:

• Age 18 years or older
• Prescribed a chemotherapy medication
• Currently taking one or more study medications (citalopram, escitalopram, venlafaxine, desvenlafaxine, codeine, oxycodone, hydrocodone, tramadol or ondansetron)

Exclusion Criteria:

• Patients who are unable to complete study materials (surveys) with or without assistance, including non-English speaking patients
• Patients receiving palliative care
• Patients taking anti-depressants for reason other than depression or anxiety, i.e. hot flash (Only applies to antidepressant cohort)
• Patients with preexisting major depressive disorder prior to cancer diagnosis (Only applies to antidepressant cohort)

Cancer patients taking selective medications for treatment of chemotherapy side effects, pain, depression and nausea.