There are several different types of antidepressants, each of which works in different ways. All of these medications are designed to affect certain chemicals or neurotransmitters in the brain that are responsible for mood, but different types affect one or more of these neurotransmitters differently. In general, antidepressants work by increasing the amount of neurotransmitters in the brain, usually by preventing them from being broken down or "recycled" in the body. How exactly this is accomplished, and how the changes in levels of neurotransmitters affect other aspects of brain chemistry, is still being investigated.
This type of medication is often prescribed to people suffering from depressive illness. The causes of depressive illness are not completely understood, but many researchers believe that neurotransmitters, including serotonin, norepinephrine, and dopamine, play a significant role. These chemicals, which are 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 stops having any effect on the brain.
Medications known as selective serotonin reuptake inhibitors (SSRIs) delay the reuptake of one of these neurotransmitters, serotonin, raising its levels in the brain. Higher levels of serotonin seem to help the brain send and receive messages more easily, which, in turn, improves mood. SSRIs are very popular because they seem to have the fewest side effects among such drugs. Additionally, those side effects tend to be mild to moderate and are transitory, usually disappearing after one to three weeks.
Tricyclic antidepressants (TCAs), work in the same manner as SSRIs, but affect the uptake of all three neurotransmitters associated with mood: serotonin, norepinephrine and dopamine. They do have more side effects, however, and can be dangerous if taken in high amounts. TCAs are not recommended to patients with heart trouble.
Monoamine oxidase inhibitors (MAOIs), an older class of antidepressants, increase levels of all three neurotransmitters by inhibiting an enzyme responsible for inactivating them. MAOIs also affect tyramine, a molecule linked 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 these drugs are not addictive and can be taken in an ongoing regimen, they are normally prescribed for a four to six month period, with most people experiencing some benefit after two to four weeks of use, and full benefits at about four months. Patients are encouraged to seek other means of relief from their depression during this period, including exercise, a healthy diet, and "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 a healthcare professional. Medications should not be mixed unless under the guidance of a medical professional. In some cases, depression can increase when patients first start taking the drugs, before they have a chance to work, and this has been linked to a higher risk of suicide in rare cases. For the majority of patients, however, these medications have played an important role in relieving depressive illness. They might also be prescribed to relieve anxiety, obsessive behavior, panic attacks and post-traumatic stress syndrome.