There are three principal types of antidepressant medications: the tricyclic drugs, the monoamine oxidase inhibitors (MAOIs), and the selective serotonin re-uptake inhibitors (SSRIs). There are also three drugs that are chemically distinct from these types and each other:

Wellbutrin, Desyrel, and Effexor. Classes differ in their mechanisms of action and side effects. However, they all have several things in common. They are effective in reducing depressive symptoms in 60 to 80 percent of the persons who use them. They also take from a month to six weeks to produce their full effects, although there can be side effects and changes in mood can occur much sooner.

In this chapter, I'll discuss the different classes of drugs before taking a closer look at the issue of side effects.

The Tricyclics
The tricyclic drugs were the first antidepressant medications. They dominated the market for more than twenty years, and are still used today, though less frequently. They work by desensitizing a receptor in the neuron that absorbs the neurotransmitters norepinephrine and dopamine into the cells. This results in higher levels of these two chemicals in the synapse, and consequent improvements in mood.

The first one in this category was imipramine hydrochloride (Tofranil). More recent additions to this group include amitriptyline hydrochloride (Elavil, Limbitrol, Endep), desipramine hydrochloride (Norpramin), doxepin hydrochloride (Adapin, Sinequan), nortriptyline hydrochloride (Pamelor, Aventyl), and protriptyline hydrochloride (Vivactil).

A serious problem with the tricyclics is their level of side effects, particularly in patients over age sixty-five. They interfere with the body's control of blood pressure, which can lead to dizziness and even fainting spells. The drowsiness they produce makes it hazardous to drive. Some patients experience arrhythmias, or irregularities in heartbeat, as well. Additional side effects include sedation, dry mouth, blurred vision, confusion, weight gain, flulike symptoms, sweating, rashes, nausea, constipation or diarrhea, difficulty with urination, impotence or impaired erection in men, inhibited orgasm in women, nightmares, and anxiety.

Due to these effects, tricyclics are not usually prescribed, except when cost is a consideration, since they are considerably cheaper than the SSRIs. Because the tricyclics are an older class of drug, their patents have already run out, and the generic brands are more competitively priced. Some doctors will prescribe either doxepin or desipramine to be taken at bedtime in order to counter the insomnia that often occurs with Prozac.

The Monoamine Oxidase Inhibitors
The monoamine oxidase inhibitors, or MAOIs, have a different mechanism of action than the other antidepressants. They work by reducing the quantity of the enzyme MAO within the synapse. The function of the enzyme is to help transport neurotransmitters, particularly norepinephrine, into the neurons. When MAO is inhibited, there is a greater supply of neurotransmitters in the synapse. This usually results in a reduction of depressive symptoms. The MAOIs seem to be particularly effective for atypical depression, in which depression is accompanied by oversleeping, overeating, and anxiety. This class of antidepressant includes phenelzine sulfate (Nardil) and tranylcypromine sulfate (Parnate).