Antidepressants are often the first treatment choice for adults with moderate or severe depression. Although antidepressant medications don't cure depression, they can help you achieve remission — the disappearance or nearly complete reduction of symptoms. Sadness, anxiety, depression-related sleep and appetite problems, concentration, and energy levels all can improve with antidepressant medications.

With scores of antidepressants available, though, finding the right one for your situation can be challenging. Understanding what a treatment plan entails and what goes into determining the right medication for you will help you sort through your options.

Precisely how antidepressants work to treat depression remains speculative. Scientists do know that antidepressants can influence brain activity through the effects they have on mood-related brain chemicals called neurotransmitters and certain nerve cell receptors. Nerve cells release neurotransmitters to communicate with other nerve cells in the brain. Neurotransmitters transmit signals across a gap (synapse) between the nerve cells.

Neurotransmitters associated with depression are serotonin (ser-oh-TOE-nin), norepinephrine (nor-ep-ih-NEF-rin) and possibly dopamine (DOE-puh-mene). Research suggests that people with depression have lower levels of one or more of these neurotransmitters.

Nerve cells send a signal and then reabsorb (reuptake) the neurotransmitters after they've communicated with other nerve cells. Antidepressants interfere with this reuptake. This results in a greater quantity of a particular neurotransmitter remaining in the synapse. This can change the activity of certain nerve cells and influence brain activity. Maintaining a higher level of neurotransmitters improves neurotransmission — the sending of those nerve impulses — which, in turn, improves your mood.

In addition, a type of antidepressant called tetracyclic antidepressants are thought to work by preventing neurotransmitters from binding with certain nerve cell receptors. This indirectly increases the levels of norepinephrine and serotonin in your brain.

Dozens of antidepressants are available, each affecting neurotransmitters in a different way. Antidepressants are typically grouped into categories, either based on when the medications came into use, their chemical structure or how they affect brain chemistry.

Here are the antidepressants that have been approved by the Food and Drug Administration (FDA) specifically to treat depression, with their generic or chemical names followed by available brand names in parentheses, and grouped by how they affect brain chemistry.

Selective serotonin reuptake inhibitors (SSRIs)

• Citalopram (Celexa)
• Escitalopram (Lexapro)
• Fluoxetine (Prozac, Prozac Weekly)
• Paroxetine (Paxil, Paxil CR)
• Sertraline (Zoloft)

Serotonin and norepinephrine reuptake inhibitors (SNRIs)

• Duloxetine (Cymbalta)
• Venlafaxine (Effexor, Effexor XR)

Norepinephrine and dopamine reuptake inhibitors (NDRIs)

• Bupropion (Wellbutrin, Wellbutrin SR, Wellbutrin XL)

Tetracyclic antidepressants

• Mirtazapine (Remeron, Remeron SolTab)

Combined reuptake inhibitors and receptor blockers

• Trazodone
• Nefazodone
• Maprotiline

Tricyclic antidepressants (TCAs)

• Amitriptyline
• Amoxapine
• Desipramine (Norpramin)
• Doxepin (Sinequan)
• Imipramine (Tofranil)
• Nortriptyline (Pamelor)
• Protriptyline (Vivactil)
• Trimipramine (Surmontil)

Monoamine oxidase inhibitors (MAOIs)

• Phenelzine (Nardil)
• Tranylcypromine (Parnate)
• Isocarboxazid (Marplan)
• Selegiline (Emsam)

The FDA normally approves a drug to treat a specific condition in a particular population. Many drugs used to treat depression in adults have been FDA approved specifically for that use.

But doctors may also prescribe drugs to treat depression that haven't actually been approved to treat depression — a practice known as off-label use. For instance, doctors often prescribe clomipramine (Anafranil) because it may improve depression even though it's FDA approved for obsessive-compulsive disorder. The same may be true of other psychiatric drugs, as well.

So among the dozens available, which antidepressant should you take?

Finding the right one might take time. Each medication has its own pros and cons, and until you try one, you won't know how it'll affect you or how well it'll work. You may need to try several antidepressants before finding the one, or the combination, that's most effective for you with the fewest side effects.

Consider your health profile
Your family doctor or psychiatrist will take into account your symptoms and their severity, your health history, other illnesses you have and lifestyle factors when determining which antidepressant to prescribe.

Your doctor will also consider your age, sex, weight and diet, mostly because of concerns about side effects. Older adults, for instance, generally tolerate the side effects of the newer antidepressants better than the side effects of the older tricyclic antidepressants. However, for some people, the older medications are more effective in treating depression.

Pregnancy also is an issue. Some psychiatric medications may pose a risk to the developing baby. Other medications may be excreted in breast milk to infants.

If any close relatives, such as a brother or sister, have taken antidepressants, their experiences could predict how well a medication will work for you or what side effects you may experience. Tell your doctor if any of your close relatives have taken antidepressants.

Make your personal preferences known
How you take an antidepressant also may influence your medication choice. Some medications come in pill form, while others come as solutions or injections. You may not be comfortable taking an antidepressant that must be injected, for instance. Or you may prefer a once-a-week medication, while someone else doesn't mind taking several doses a day.

Cost is also a consideration. Some antidepressants are available in a generic form, which is generally cheaper than a brand-name version. Newer versions of a drug are sometimes more expensive than the original. But watch out — those newer versions aren't necessarily more effective.

Once you and your doctor have selected an antidepressant for you to try, it may take four to eight weeks to determine its full effectiveness. With some medications, you can take the full dosage immediately. With others, you may need to gradually increase your dose.

If you have no improvement at all in your symptoms after six weeks, it may be time to try a different antidepressant or add a second medication to augment your treatment. You may have to taper off of one medication before starting another, because potentially dangerous drug interactions and withdrawal-like symptoms can occur from an abrupt switch.

In rare cases, antidepressants simply might not work for you. You may need to consider other forms of treatment, such as psychotherapy to help cope with social or other life stressors, or electroconvulsive therapy if your depression is severe or life-threatening.

Finding the right antidepressant and the correct dosage can take time. Talk to your doctor if you're having trouble coping with the wait.