Certain brain chemicals called neurotransmitters are associated with depression, including the neurotransmitters serotonin (ser-oh-TOE-nin) and norepinephrine (nor-ep-ih-NEF-rin). Research suggests that abnormalities in neurotransmitter activity can affect mood and behavior.

Combined reuptake inhibitors and receptor blockers are dual-action antidepressants. That is, they act on brain cells in two ways — both by inhibiting the reabsorption (reuptake) of neurotransmitters into nerve cells and by blocking nerve cell receptors. This leaves more of these neurotransmitters available in the brain, thereby boosting mood.

Here are the combined inhibitors and blockers that have been approved by the Food and Drug Administration specifically to treat depression:

• Trazodone
• Nefazodone
• Maprotiline

These antidepressants are available only in generic form. The brand-name versions have been withdrawn from the market for various reasons.

Some of these medications may also be used to treat conditions other than depression.

Side effects of combined inhibitors and blockers include:

• Dry mouth
• Dizziness
• Drowsiness
• Lightheadedness
• Nervousness
• Nausea
• Constipation
• Weakness
• Vision problems
• Confusion
• Headache

Trazodone has been associated with priapism — persistent, usually painful erections not associated with sexual arousal. If this occurs, seek medical treatment immediately. Many of those cases have required surgical correction, resulting in permanent impairment of erectile function or impotence.

In rare cases, nefazodone (nef-AY-zoe-dohn) can cause life-threatening liver failure. Don't take it if you already have liver problems. Know the signs and symptoms of possible liver dysfunction, such as yellowing of your skin or the whites of your eyes, unusually dark urine, loss of appetite, nausea or abdominal pain. Contact your doctor immediately if you experience any of these problems. In addition, be sure to talk to your doctor before using pimozide, carbamazepine, triazolam or MAOIs if you're taking nefazodone.

Maprotiline has been associated with seizures, so people with a history of seizures usually shouldn't take this medication. Also, maprotiline shouldn't be used in combination with MAOIs.

In some cases, antidepressants may be associated with worsening symptoms of depression or suicidal thoughts or behavior, particularly early in treatment or when you change your dosage. Be sure to talk to your doctor about any changes in your symptoms. You may need more careful monitoring at the beginning of treatment or upon a change in treatment, or you may need to stop the medication if your symptoms worsen.