Depression is a common mental health disorder that occurs in 15% of the population at some stage in their lives. Depression has a lifetime prevalence of 12-20%, with women are affected 1.5 times as much as men. The core features of a depressive episode are pervasive low mood, lack of energy, lack of pleasure and an inability to enjoy life. More severe episodes are additionally associated with sleep disturbance, loss of appetite and weight loss, impaired concentration, self-neglect, retardation, hopelessness, negative thoughts and even delusions, as well as prominent suicidal ideas and suicidal acts.
With a population of 4.8 million people, 6,000 require hospitalisation annually for depression in Ireland, accounting for 30% of in-patient admissions to mental health services. For some people a depressive episode may be self-limiting and not require any major intervention, whereas others may need to seek help from their GP or a specialist psychiatry service.
According to the World Health Organisation, depression is now the leading cause of disability worldwide. In Europe, depression is the most costly brain disorder, accounting for 1% (€118 billion annually) of the total EU economy. Approximately 50% of people who experience one depressive episode will have further episodes, with five to nine episodes in their lifetime. Depression is thus a major national and global public health concern because of its high prevalence and societal costs. Additionally, depression can lead to chronic disability, is a risk factor for both dementia and stroke in later life, and 6% will die by suicide.
Commonly used treatments for depression include medications (e.g. antidepressants) and psychological talking therapies. Unfortunately, about third of people with moderate to severe depression do not respond sufficiently well to such standard therapies and have "treatment-resistant" depression. Even following successful antidepressant therapy for acute episodes, relapse rates are high, ranging 40-70%. By the time a patient has tried four or more different antidepressant, alone or in combination, the chance of remission is about 10% with the next treatment. However, for such treatment-resistant patients, the chances of recovery with electroconvulsive therapy (ECT) are about 50% and are even higher for very severe and psychotic depressive episodes. We are also currently investigating the antidepressant efficacy of ketamine, a dissociative anaesthetic.
