The Taste-Mood Diagnostic Study

Inclusion Criteria: * Patients with a diagnosis of previously untreated Major Depressive Disorder (MDD) of at least 3 weeks duration or new or recurrent MDD untreated before this episode (patients who have previously received treatment for MDD must have stopped taking antidepressant medication at least six weeks prior to entering the trial); * Patients requiring pharmaceutical intervention as a treatment for MDD; * Not suffering from any significant other mental or physical illness, such as confirmed psychosis, or end of life care. * Receiving stable medical therapy for 30 days or longer before screening assessments; * Be willing and able to comply with all visits and study related procedures; * Not infected with coronavirus or needing to self-isolate * Understands the study requirements and the treatment procedures and is able to provide written informed consent. Exclusion Criteria: * Already on antidepressant medication; * Known or suspected hypersensitivity or intolerance to any probes, or any of their excipients; * Relevant history or presence upon clinical examination, of cardiac, ophthalmologic, gastro-intestinal, hepatic, or renal disease or other condition known to increase risk of side effects of the probe drugs. This exclusion criterion is determined by the Site Investigator; * Have a history or presence of neurological or confounding psychiatric conditions (such as stroke, traumatic brain injury, epilepsy, space occupying lesions, multiple sclerosis, Parkinson's disease, vascular dementia, transient ischemic attack, or schizophrenia), * Patients with a diagnosis of chronic pain. * Participation in another trial concurrently or within 30 days preceding enrolment that is deemed to interfere with this trial; * Patients who are pregnant, or who are likely to become pregnant, will be excluded from the trial, as will breastfeeding mothers; * Patients using supplements containing psychoactive herbs (for example St Johns Wort or 5-HTP (5-Hydroxytryptophan, also known as oxitriptan); * Patients regularly using psychoactive stimulants and recreational drugs (for example MDMA (ecstasy/ methyl enedioxy methamphetamine), amphetamine, LSD (lysergic acid diethylamide), cocaine); * Patients infected with coronavirus, or who are advised to self-isolate * Patients who are unable or unwilling to comply with study procedures.