Dosage of antidepressants varies, depending on the type of drug and the person’s body chemistry, age, and, sometimes, body weight. Traditionally, antidepressant dosages are started low and raised gradually over time until the desired effect is reached without the appearance of troublesome side effects. Newer antidepressants may be started at or near therapeutic doses.
Early antidepressants. From the 1960s through the 1980s, tricyclic antidepressants (named for their chemical structure) were the first line of treatment for major depression. Most of these medications affected two chemical neurotransmitters, norepinephrine and serotonin. Though the tricyclics are as effective in treating depression as the newer antidepressants, their side effects are usually more unpleasant; thus, today tricyclics such as imipramine, amitriptyline, nortriptyline, and desipramine are used as a second- or third-line treatment. Other antidepressants introduced during this period were monoamine oxidase inhibitors (MAOIs). MAOIs are effective for some people with major depression who do not respond to other antidepressants. They are also effective for the treatment of panic disorder and bipolar depression. MAOIs approved for the treatment of depression are phenelzine (Nardil), tranylcypromine (Parnate), and isocarboxazid (Marplan). Because substances in certain foods, beverages, and medications can cause dangerous interactions when combined with MAOIs, people on these agents must adhere to dietary restrictions. This has deterred many clinicians and patients from using these effective medications, which are in fact quite safe when used as directed.
The past decade has seen the introduction of many new antidepressants that work as well as the older ones but have fewer side effects. Some of these medications primarily affect one neurotransmitter, serotonin, and are called selective serotonin reuptake inhibitors (SSRIs). These include fluoxetine (Prozac), sertraline (Zoloft), fluvoxamine (Luvox), paroxetine (Paxil), and citalopram (Celexa).
The late 1990s ushered in new medications that, like the tricyclics, affect both norepinephrine and serotonin but have fewer side effects. These new medications include venlafaxine (Effexor) and nefazadone (Serzone).
Cases of life-threatening hepatic failure have been reported in patients treated with nefazodone (Serzone). Patients should call the doctor if the following symptoms of liver dysfunction occur – yellowing of the skin or white of eyes, unusually dark urine, loss of appetite that lasts for several days, nausea, or abdominal pain.
Other newer medications chemically unrelated to the other antidepressants are the sedating mirtazepine (Remeron) and the more activating bupropion (Wellbutrin). Wellbutrin has not been associated with weight gain or sexual dysfunction but is not used for people with, or at risk for, a seizure disorder.
Each antidepressant differs in its side effects and in its effectiveness in treating an individual person, but the majority of people with depression can be treated effectively by one of these antidepressants.