Depression is a common condition. It may be situational, or may be due to an imbalance of hormones in the brain (Clinical Depression). Although there is no laboratory test for depression, and experienced clinician can make diagnosis based on history and observation, and recommend medication to correct a likely imbalance.
The most commonly prescribed antidepressants are currently the Selective Serotonin Reuptake Inhibitors (SSRI). This type of antidepressant has mostly replaced older ones (e.g. Monoamine Oxidase Inhibitors (MAOI), Tricyclic Antidepressants (TCAs)). The SSRIs are generally considered to be more effective than the older types, and are typically considered safer and therefore preferable for use in depressed patients who may feel suicidal. Prozac (fluoxetine) was the first SSRI in the United States (Luvox (Fluvoxamine) being the first worldwide).
One theory of depression is a depressed level of serotonin (there may also be an connection with an imbalance in other neurotransmitters such as dopamine and/or norepinephrine). SSRIs act by inhibiting the reuptake of serotonin elevating available serotonin levels (it does not cause more serotonin to be created). Antidepressants (including SSRIs) can alter the level of more than one neurotransmitter simultaneously. The affinity for other neurotransmitters will vary depending on the particular drug considered. Though some types of antidepressants have been designed to have a high affinity for multiple neurotransmitters (e.g. Effexor (venlafaxine) which inhibits the reuptake of both serotonin and norepinephrine).
Antidepressants usually take 2 to 6 weeks for take effect. Though treatment with an antidepressant should be reassessed at regular intervals (e.g. every couple of months) to see if continued usage is warranted.
Common side effects of SSRIs include (but are not limited to) dry mouth, nausea, sedation, headache, sweating, GI issues, weight gain/loss and issues with libido. These effects usually subside within a couple weeks, though the weight and libido issues may persist throughout the duration of treatment.
Some people may experience an increase in impulsivity or suicidal ideation with these medications. Thus, the prescribing physician should be contacted upon any such out of character mood or conduct.
Caution should be used when discontinuing an antidepressant. The dosage should be reduced gradually over time (dependant on the particular drugs half-life) to reduce the chances or severity of symptoms of a discontinuation syndrome.