Medications called antidepressants work to normalize brain chemicals called neurotransmitters, notably serotonin, norepinephrine, and dopamine. Scientists studying depression have found that these chemicals, and possibly others, are involved in regulating mood, but they are unsure of exactly how they work.

The newest and most popular types of antidepressant medications are called selective serotonin reuptake inhibitors (SSRIs) and serotonin and norepinephrine reuptake inhibitors (SNRIs). SSRIs include fluoxetine (Prozac), citalopram (Celexa) and several others. SNRIs include venlafaxine (Effexor) and duloxetine (Cymbalta). Another newer antidepressant that is different from both SSRIs and SNRIs but is very popular is bupropion (Wellbutrin). 

Older antidepressants, called tricyclics and monoamine oxidase inhibitors (MAOIs), are still used sometimes, too. However, these older antidepressants are not as popular as the newer ones because they tend to have more side effects. However, medications affect everyone differently so talk with your doctor to decide which type is best for you. 

People taking MAOIs must follow strict food and medicine guidelines to avoid potentially serious interactions. They must avoid substances that contain high levels of the chemical tyramine which is found in many cheeses, wines, and pickles and in some medications including decongestants. MAOIs interact with tyramine in a way that may cause a sharp rise in blood pressure, possibly leading to a stroke. The development of a new MAOI skin patch may help reduce these risks. A doctor should give a patient taking an MAOI a complete list of foods, medicines, and substances to avoid.

MAOIs can also react with SSRIs to produce a serious condition called "serotonin syndrome," which can cause confusion, hallucinations, increased sweating, muscle stiffness, seizures, changes in blood pressure or heart rhythm, and other potentially life threatening conditions. MAOIs should not be taken with SSRIs.

Caution is required when combining any serotonergic medication (not just MAOIs) with SSRIs. For example, in 2006 the FDA issued specific warnings against using triptans that are commonly-prescribed to treat migraine headaches together with SSRIs or SNRIs. Using these medications together can cause serotonin syndrome. 

For all types of antidepressants, patients must take regular doses for at least four to six weeks, sometimes longer, before they are likely to feel the full benefit. They should continue taking the medication for an amount of time specified by their doctor, even if they are feeling better, to prevent the depression from returning. 

Stopping medication should be done only under a doctor's supervision. They need to be gradually stopped to give the body time to adjust. Although they are not habit-forming or addictive, antidepressants should not be stopped abruptly because that can cause withdrawal symptoms or lead to a relapse. Some people, such as those whose depression is chronic or keeps returning, may need to stay on the medication for a long time. 

Older adults who are experiencing their first episode of depression also may want to stay on antidepressant medication for a while, even if their symptoms have disappeared. Recent research shows that patients age 70 and older who took antidepressant medication for two years after they became symptom-free were 60 percent less likely to experience a relapse than those who stopped taking the medication. 

If one medication does not work, patients should be willing to try another. Research has shown that patients who do not get well after taking a first medication increase their chances of getting well after switching to a different medication or adding another medication to their first one. 

The most common side effects of antidepressant medications include headache, nausea, insomnia or nervousness, agitation or a jittery feeling, and sexual problems. Often they are mild and temporary. However, any unusual reactions or side effects that interfere with normal functioning should be reported to a doctor immediately.

For older adults who are already taking several medications for other conditions, it is important to talk with a doctor about any adverse drug interactions that may occur while taking antidepressants.

In some rare cases, antidepressant medications may lead to suicidal thoughts or actions. However, there is no evidence that they may have this unintended effect among older adults. 

In addition to antidepressants, some people use the herb St. John's wort to treat mild to moderate depression. A bushy, wild-growing plant with yellow flowers, the herb has been used for centuries in many folk and herbal remedies. Today in Europe, it is widely used to treat mild to moderate depression. In the United States, it is one of the top-selling botanical products. 

In a study funded by the National Institutes of Health, the herb was found to be no more effective than a placebo (sugar pill) in treating adults suffering from major depression. 

Other research has shown that St. John's wort can interact unfavorably with other drugs. The herb interferes with certain drugs used to treat heart disease, depression, seizures, certain cancers, and organ transplant rejection. Because of these potential interactions, older adults should always consult with their doctors before taking any herbal supplement. 

Another product sold as a dietary supplement, S-adenosyl methionine (SAMe), has shown promise in controlled trials as helpful when added to an SSRI antidepressant that is only partially effective.