With well over two dozen traditional antidepressants available in the US, and an ever-growing list of other psychotropic compounds with apparent antidepressant properties, pharmacological options for treating clinical depression today are broad and vast. However, recent findings suggest that the magnitude of efficacy for most antidepressants compared with placebo may be more modest than previously thought.1Most depressed patients do not respond fully to a first antidepressant trial, and with each consequent trial, there is less chance of symptom remission.2 About one-third of patients receiving long-term treatment report persistent moderate-to-severe depression.3 Hence, there remains more than a little room for improvement.
Since the late 1950s, the traditional view of treating depression has focused on the role of monoamines (serotonin, norepinephrine, and dopamine) as the main targets for medications. Newer treatments are looking beyond effects on monoamines as potential strategies to leverage depressive symptoms.
A major challenge for progress in novel pharmacotherapies has been our lack of a full understanding about the causes of depression. Advances in functional neuroimaging and genetic markers have begun to shed new light on brain regions and pathways associated with aberrant neural functioning in depression, but not in ways that have led to treatments aimed at remedying its pathogenesis. This makes it hard to think of antidepressant medications as “treating” the pathophysiology of depression (as when antibiotics eliminate the cause of an infection); rather, antidepressant relieve symptoms by counteracting or compensating for depression’s consequences (as when diuretics alleviate peripheral edema regardless of its etiology).
Gone are the days of oversimplified theories that depression is caused by a “chemical imbalance.” More likely, depression involves changes in brain architecture and the interplay of complex circuits in which chemicals, or neurotransmitters, are the messengers of information, rather than the causes of faulty functioning. Table 1 summarizes some of the major conceptual shifts that have occurred in thinking about the probable causes of depression (or at least its neurobiological context), which sets the stage for new ways to consider innovative treatment strategies. Looking beyond the role of monoamines as treatment targets in depression, a number of novel therapeutic strategies have begun to receive growing interest in preclinical and clinical trials. Key points about emerging novel depression pharmacotherapies are summarized in Table 2, and described more fully below.