Amitriptyline is a tricyclic antidepressant (TCA). It is the most widely used TCA and is an efficacious treatment for major depressive disorder (clinical depression). Amitriptyline is used for a number of medical conditions including major depressive disorder (MDD) which is its only FDA-labelled indication. This is also a TGA- and MHRA-labelled indication. Some evidence suggests that amitriptyline may have superior efficacy compared to other antidepressants, including the SSRIs. Although it is rarely used as a first-line antidepressant nowadays due to its high degree of toxicity in overdose and generally poorer tolerability than the newer antidepressants such as the selective serotonin reuptake inhibitors (SSRIs) and serotonin-norepinephrine reuptake inhibitors (SNRIs). It is TGA-labelled for migraine prophylaxis, as it is also is in cases of neuropathic pain disorders, fibromyalgia and nocturnal enuresis.