Certain brain chemicals called neurotransmitters are associated with depression, including the neurotransmitters norepinephrine (nor-ep-ih-NEF-rin) and dopamine (DOE-puh-mene). Research suggests that abnormalities in neurotransmitter activity can affect mood and behavior.

Norepinephrine and dopamine reuptake inhibitors (NDRIs) are a type of antidepressant medication that increases the levels of both norepinephrine and dopamine by inhibiting their reabsorption into cells. As with other antidepressants, the precise mechanism of action isn't clear. But it's thought that these increased levels help enhance neurotransmission — the sending of nerve impulses — and thereby improve and elevate mood.

Here is the only NDRI that has been approved by the Food and Drug Administration specifically to treat depression, with its generic or chemical name followed by available brand names in parentheses:

• Bupropion (Wellbutrin, Wellbutrin SR, Wellbutrin XL)

Bupropion (bu-PRO-pe-on) is available in several forms: an immediate-release form taken three times a day; a slow-release, or sustained- release, (SR) form that requires taking medication twice a day, and an extended-release (XL) form that requires only a once-a-day dose. Zyban, another brand of bupropion, is available as an anti-smoking medication, not as an antidepressant.

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

Side effects of NDRIs include:

• Loss of appetite
• Weight loss
• Headache
• Dry mouth
• Skin rash
• Sweating
• Ringing in the ears
• Shakiness and nervousness
• Stomach pain
• Agitation
• Constipation
• Anxiety
• Dizziness
• Trouble sleeping
• Muscle pain
• Nausea and vomiting
• Fast heartbeat
• Sore throat
• More frequent urination

Bupropion can increase blood pressure in some people, so regular monitoring is important. The risk of developing high blood pressure may increase if you also use nicotine replacement therapy, such as a nicotine patch, to help you stop smoking.

There's a small chance that taking bupropion can cause a seizure if you've had previous seizures, a head injury or a nervous system tumor, or if you've had an eating disorder, such as bulimia or anorexia. Because of that, don't take this medication if you have a history of seizures or eating disorders or if you're abruptly discontinuing use of alcohol or sedatives. Be sure to tell your doctor about your past medical issues.

Also, because of potentially dangerous medication interactions, be sure your doctor knows about any current or previous use of monoamine oxidase inhibitors (MAOIs). Also tell your doctor if you have severe liver cirrhosis because Wellbutrin can cause liver problems. In addition, don't take Zyban while you're being treated with any form of Wellbutrin.

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.