Three years ago Cincinnati Reds pitcher Pete Harnisch began losing interest in food, sleeping fitfully and withdrawing from friends and teammates. His strength and confidence crumbled, and he quit pitching. "It was a real tough time for me," the ballplayer says.

A doctor diagnosed depression, and put Harnisch on Prozac, but Harnisch didn't like the side effects. So next, his doctor prescribed Paxil. In a matter of weeks, Harnisch felt better. After six months, he was able to go off the medication. These days the 34-year-old pitcher is back to his fighting weight -- 228 pounds -- and back at work. The Reds have indicated they'll exercise their $3.75 million option on his contract for another year.

All too often, recovering from depression demands an athlete's courage, stamina and persistence. No more than half the people who try a given antidepressant see improvement. Like Harnisch, the rest must try one or more other drugs before they find a medication that works. In the process, they may experience side effects ranging from sexual dysfunction to flatulence.

"All of the antidepressants work. They just don't all work for everybody," says Lydia Lewis, executive director of the National Depressive and Manic-Depressive Association, herself a chronic depression sufferer. "You have to have the courage to continue to try until you find the drug, or the combination of drugs, that works for you."

"What's wildly salutary for one person can be disastrous for another," agrees Bruce S. Victor, M.D., associate clinical professor of psychiatry at the University of California at San Francisco. "The reason is that the introduction of any antidepressant is a chemistry experiment, and not just with the chemistry of the drug but with how the drug interacts with a patient's individual body chemistry."

Alan F. Schatzberg, M.D., professor and chairman of psychiatry and behavioral sciences at Stanford University, says patients may give up on antidepressant therapy because they're not getting any better -- or because, even if they are getting better, they can't stand the side effects.

But Schatzberg counsels perseverance. "If one antidepressant therapy doesn't work, you should try another," he says.

And, if necessary, another. "If you only rely on the first treatment, you're selling yourself short," says Madhukar Trivedi, M.D., a psychiatrist at the University of Texas. Trivedi served on a federal committee that developed depression treatment guidelines for primary-care physicians.

There are three main classes of antidepressants: The tricyclic antidepressants, the monoamine oxidase (MAO) inhibitors, and the selective seratonin reuptake inhibitors (SSRIs). Several new, chemically unique drugs don't fit into any of these categories. The drugs have similar effectiveness and similar rates of side effects. But there are profound differences in the types of side effects.

"Because all of the antidepressants are equally effective, choice should be determined by side-effect profile," says Brian Doyle, M.D., a psychiatry professor at Georgetown University Medical School in Washington, D.C. "You try to match the side-effect profile to the patient's needs."

For example, if you're depressed, anxious, irritable and can't sleep, you might do better on Paxil than Prozac. Paxil can be mildly sedating, while Prozac can have the opposite effect. If, on the other hand, you're depressed, lethargic and have trouble getting out of bed, Prozac may make more sense.

All classes of antidepressants act on neurotransmitter receptors -- not just in the brain, but throughout the body, including the gastrointestinal tract and the genitourinary tract. Even among drugs in the same class, these effects can differ tremendously. Compared with other SSRIs, for example, Zoloft tends to cause more nausea and diarrhea.

"So I stay away from Zoloft in patients with a sensitive gut, irritable bowel syndrome or colitis," Doyle says.

Sexual dysfunction can be among the most troubling side effects of depression treatment. Just when the therapy seems to be improving many other aspects of life, some men begin to experience diminished desire for sex, find it difficult to become sexually aroused, or have trouble achieving orgasm. The problems can occur with MAO inhibitors, tricyclics, SSRIs and Effexor, affecting up to 20 percent of men and 2 to 3 percent of women. Sexual side effects are infrequent with Serzone, Wellbutrin and Remeron.

Antidepressant therapy may also lead to weight gain -- defined as a 7 percent gain over your usual weight. Paxil and Remeron appear to be among the worst offenders, while Effexor and Wellbutrin do not seem to cause weight gain -- and may result in some weight loss.

Co-existing health problems sometimes help to guide the choice of an antidepressant. Wellbutrin, for example, is an alternate medication for attention deficit disorder (ADD). Marketed under the brand name Zyban, the drug is also used to help smokers give up tobacco. If you're depressed and smoke or have ADD, therefore, Wellbutrin may be a good choice.

Earlier this year, a Mayo Clinic psychiatrist described four patients who experienced jaw clenching, headaches, tooth grinding and broken teeth after starting Zoloft for relief of depression and anxiety. Three other recent reports in the literature describe similar side effects in patients taking Paxil and Prozac.

So if you grind your teeth, you might want to avoid an SSRI.

But if you suffer from obsessive-compulsive tendencies, panic attacks or extreme shyness, an SSRI may be a great choice. SSRIs have proved effective in treating each of these disorders, in addition to depression.

Antidepressant therapy should produce some improvement in four to six weeks. If you don't improve, talk with your doctor about switching to another drug.

If you don't improve on a second drug, consider asking for a referral to a psychiatrist. "There are tricks a psychiatrist knows that a primary care physician wouldn't know to try," says Dean MacKinnon, M.D., a psychiatrist at The Johns Hopkins University School of Medicine in Baltimore.

"It's worth it to hang in there," Doyle says. "When you find the right treatment, it's fabulous. The patient's life is just revolutionized."

For a first episode of depression, the American Psychiatric Association recommends continuing antidepressant therapy for at least nine months after depression symptoms have improved. For a second episode, therapy should continue for 18 months to two years. Three to five years of treatment is needed for a third episode, and lifelong therapy may be needed for patients who experience more than three episodes, according to the APA.

"There is definitely a light at the end of the tunnel," Reds' pitcher Harnisch says. "No matter what it may seem."

Reducing the Side Effects of Antidepressants

Here are some common side effects of antidepressants and ways to handle them.

Sedation: Take medication in the evening rather than the morning, or ask your doctor about adjusting the dose.

Insomnia: Take medication in the morning rather than the evening, or ask your doctor about adjusting the dose, changing the medication or adding another drug.

Other sleep disturbances: All SSRIs, at least initially, tend to make people sleep lightly and have more vivid dreams. These side effects often improve with time. If they don't, talk with your doctor about a change in dose or medication.

Dizziness, difficulty concentrating, dry mouth: Side effects that occur early are often temporary, and go away as the medication takes full effect and your body adapts.

Excessive sweating: At night, keep the temperature in your bedroom cool and sleep with only a light cover on your bed. During the day, dress in layers so you can remove garments as needed. This side effect is often temporary.

If the sweating is so severe that interrupts sleep or causes embarrassment during the day, talk with your doctor about changing your dose or medication, or adding another medication to combat the sweating.

Nausea: Take medication with food, or talk with your doctor about a lower dose. Stomach upset tends to improve with time. If it doesn't, cisapride is sometimes prescribed.

Sexual side effects: Talk with your doctor about decreasing or skipping doses from Thursday through Sunday night, for a "holiday" from side effects over the weekend. Adding Wellbutrin, BuSpar, Remeron or Serzone can reverse sexual side effects. Low-dose Ritalin or Viagra are also effective.

Tooth-grinding (bruxism): Talk with your doctor about a change in dose or medication, or about adding the anti-anxiety agent BuSpar.

Withdrawal symptoms: Though not a sign of addiction, withdrawal symptoms can occur when antidepressants are stopped abruptly. Symptoms include nausea, headache dizziness, drowsiness, light-headedness, malaise, agitation or anxiety, sweating, diarrhea, dry mouth, insomnia and more. To avoid such symptoms, taper off a drug slowly when discontinuing it for good -- and avoid skipping doses during therapy.

Sources: National Depressive and Manic-Depressive Association, Brian Doyle, M.D., Dean MacKinnon, M.D., Bruce S. Victor, M.D.