Antidepressants are often prescribed to people suffering from depressive illness. Depressive illness is caused by a decrease of certain chemicals or neurotransmitters in the brain that are responsible for mood. Antidepressants stimulate chemical changes that increase the levels of these neurotransmitters. Three main neurotransmitters associated with mood are serotonin, norepinephrine and dopamine. Different antidepressant medications affect one or more of these neurotransmitters.

Neurotransmitters released from nerve cells in the brain only have a short time to relay their message to another cell before enzymes destroy them or they are taken back up by the cell. This process is referred to as reuptake. Once reuptake occurs, the neurotransmitter ceases to have any affect on the brain.

In people suffering from depressive illness fewer of these neurotransmitters are being produced. Therefore antidepressant medications known as selective serotonin reuptake inhibitors (SSRIs) delay the reuptake of one of these neurotransmitters, serotonin, thus raising levels in the brain. With more natural levels of serotonin in the brain, mood is elevated from the depressed state to a more normal state of mind. SSRIs are very popular because they seem to have the least side-effects among antidepressants. Additionally, side-effects tend to be mild to moderate and are transitory, usually disappearing after 1-3 weeks. Some brand names of SSRIs are Zoloft, Prozac, Paxil and Lexapro.

Tricyclic antidepressants (TCAs), work in the same manner but affect the uptake of all three neurotransmitters associated with mood: serotonin, norepinephrine and dopamine. However TCAs have more side-effects and can be dangerous if overdosed. TCAs are not recommended to patients with heart trouble. Some tricyclic antidepressant brand names are Allegron, Tryptizol, Anafranil and Ortrip.

Monoamine oxidase inhibitors (MAOIs), an older class of antidepressants, also increase levels of all three neurotransmitters by inhibiting an enzyme responsible for inactivating them. However, MAOIs also affected tyramine, a molecule inked to blood pressure. As a result anyone taking MAOIs must stick to a very strict diet that forbids a variety of common foods like cheeses, yogurt, certain meats, bananas, and many more foods. Failure to do so can lead to a hypertensive crisis and may result in death. MAOIs also interact with many medications and are no longer widely prescribed.

Although antidepressants are not addictive and can be taken in an ongoing regimen, they are normally prescribed for a 4-6 month period, with most people experiencing some benefit after 2-4 weeks of use, and full benefits at about 4 months. Patients are encouraged to seek other means of relief from their depression during this period, including exercise, a healthy diet, and in some cases "talk" therapy to work through any external cause for the depression.

Specific side-effects vary among the different groups of antidepressants and should be discussed with your physician. Antidepressant medications should not be mixed unless your doctor tells you to do so. In some cases depression can increase at the onset of taking an antidepressant until it has had a chance to work, and in rare cases this has reportedly been linked with suicide in those intolerant of these medications. However, for the vast majority of patients taking antidepressants they have played an important role in relieving depressive illness.

Antidepressants might also be prescribed to relieve anxiety, obsessive behavior, panic attacks and post-traumatic stress syndrome.