Endogenous Depression is an atypical sub-class of the Mood Disorder, Clinical Depression (A.K.A. Major Depressive Disorder). Endogenous Depression includes patients with treatment-refractory, unipolar, non-psychotic, Major Depressive Disorder, characterized by a dysregulation of the Endogenous Opioid System and NOT of the Monoaminergic System. Patients who fall in this sub-class typically respond very well to synthetic opioids which act on the μ-opioid receptors and thought to result in increased serotonin production and norepinephrine reuptake inhibition, including Tramadol, Tapentadol, Buprenorphine, and other similar, synthetic, atypical, opioid analgesics. However, due to the addictive qualities and "taboo" nature opioids have in the eyes of the general public, doctors have been reluctant to delve into research on or treatments for Endogenous Depression, and therefore, patients who suffer the condition usually go untreated.[1][2]
It is also thought that Endogenous Depression is a mood disorder that affects some people from birth and is believed to be a genetic condition. A sufferer is prone to become depressed on the advent of traumatic events, exhaustion or when under high levels of stress and may not be aware of the disorder until confronted by symptoms of depression for the first time.
Depressive episodes can occur at any age, but despite the predisposition may never become a serious problem. The severity of depression resulting from a diagnosis can vary greatly, from mild to severe. Worsening of a persons mood may not be triggered by any external element. It is hard to determine its endogenous origin. It is often the case that a sufferer first confronted with life events that might trigger depressive condition and when no particular source of the mood disorder is found, the depression is considered to be endogenous.
Endogenous Depression was initially considered valuable as a means of diagnostic differentiation with Reactive depression. While the latter's onset could be attributed to adverse life events and treated with talk therapy, the former would indicate treatment with antidepressants[3]. Indeed, this view of endogenous depression is at the root of the popular view that mood disorders are a reflection of a 'chemical imbalance' in the brain. More recent research has shown that the probability of an endogenous depression patient experiencing an adverse life event prior to a depressive episode is roughly the same as for a Reactive depression patient and the efficacy of antidepressant therapy bears no statistical correlation with the patient's diagnostic classification along this axis[4] .