Major depressive disorder (MDD) is a neurological disorder that affects about 17% of Americans. There is a solid amount of evidence that MDD is about twice as common in women as in men, but the reason for this is unknown. MDD frequently co-occurs with other neurological disorders such as ADD, ADHD, PTSD, and anxiety. These co-occurrences can make diagnosis and treatment of the disorders difficult.
There is no single cause for MDD, and often times it can be due to multiple factors. There is evidence that a family history of MDD can increase one's risk of having MDD, but the mechanism behind this is unknown. It may be due to genetics, environment, or both. MDD can be caused by events such as abuse, conflict, or the death of a loved one. It can also have medical causes such as the use of certain medications (such as β blockers) or coexistence with certain illnesses.
Symptoms of MDD can vary. They include agitation, restlessness, irritability, difficulty concentrating (all also symptoms of ADHD!), fatigue, and difficulty sleeping. The more emotional symptoms of depression are feelings of hopelessness, helplessness, and worthlessness. People suffering from MDD may also experience loss of interest, isolation, intense anger, and even suicide.
Treatments of MDD include medication and psychotherapy. The most prescribed antidepressants are selective serotonin re-uptake inhibitors (SSRIs), such as fluoxetine and sertraline. Fluoxetine is the only antidepressant that is FDA approved for use in children and teenagers. SSRIs function by inhibiting serotonin re-uptake into the presynaptic cell. This increases the concentration of serotonin in the synaptic cleft. Serotonin functions in the CNS by regulating sleep, appetite, and mood. A 2010 study, however, indicated that SSRIs have little to no benefit (relative to placebo) in patients with mild cases of MDD.