How Do Antidepressants Affect the Brain?

If you're struggling with major depressive disorder, obsessive compulsive disorder, or another mental health condition, you've probably thought about using antidepressants. It's not uncommon for people considering, or even currently taking, antidepressants to ask questions like, "What do antidepressants do to the brain?" and "Do antidepressants permanently alter brain chemistry?" Knowing how antidepressants work with your brain chemistry can help you better understand how these medications may help you.

Many people have found relief from their symptoms by taking antidepressants. Scientists think antidepressants enhance the brain's ability to transmit signals that regulate moods. However, scientists still don't know precisely how the medications work. One theory is that people with depression have low levels of chemicals called neurotransmitters. Antidepressants may correct these chemical imbalances. Or, they may improve brain signaling by promoting the growth of new cells and connections in the brain.

How Does the Brain Transmit Signals?

Human brains are made up of approximately 100 billion cells. Between each cell are gaps called synapses. To transmit signals across synapses, brain cells secrete neurotransmitters. Neurotransmitters ferry across the synapses and are absorbed by neighboring brain cells. That stimulates these brain cells to secrete neurotransmitters of their own, which, in turn, activates their neighbors. In this way, messages are relayed through the vast network of brain cells. But brain cells also need to shut off signals. They have two ways of doing that: they can reabsorb excess neurotransmitters floating in the synapses, or they can break down and get rid of excess neurotransmitters. There are several kinds of neurotransmitters, including serotonin, dopamine, and norepinephrine. To work as efficiently as possible, different types of antidepressants have been developed to act on different neurotransmitters.

How Do Antidepressants Affect the Brain?

Many antidepressants are so-called "reuptake inhibitors." Ordinarily, brain cells make molecules that bind up excess neurotransmitters in synapses and recycle them. The neurotransmitters fit perfectly into these molecules, like keys into locks. Uptake inhibitors slip into molecules first, blocking neurotransmitters from getting in. As a result, more neurotransmitters remain in the synapses and increase the chances of stimulating neighboring cells. As their names suggest, selective serotonin reuptake inhibitors (SSRIs) block the reuptake (breakdown) of serotonin in the brain. Serotonin and norepinephrine reuptake inhibitors (SNRIs) block the reuptake of both neurotransmitters. NDRIs are norepinephrine and dopamine reuptake inhibitors. Tricyclics and tetracyclics (TCAs) work similarly, but they are used less frequently because they have more potential side effects.

Other types of antidepressants work differently. Serotonin antagonist and reuptake inhibitors (SARIs) not only block the reuptake of serotonin, but they also help prevent serotonin from binding at certain sites, leaving more to act as messengers between neighboring brain cells. Monoamine oxidase inhibitors (MAOIs) maintain higher levels of neurotransmitters by inhibiting an enzyme that breaks them down.That said, emerging studies suggest that antidepressants may improve brain signaling by stimulating new growth of brain cells and expanded brain cell networks. Like cities and the roads connecting them, parts of the brain and networks linking them are continually evolving. Over time, they deteriorate and get repaired, re-routed, or expanded. This continual rebuilding and rewiring of the brain is a natural process called neuroplasticity. Antidepressants may aid this process.

Antidepressants are designed to alter brain chemistry to alleviate symptoms—thus, they do so while you are taking them. They may promote potentially beneficial structural brain changes, as well. As impressive as it may be, the brain's neuroplasticity isn't always positive. It's important to realize that depression itself has been shown to alter brain chemistry and cause structural brain changes. Antidepressants are intended to improve your brain chemistry and help reverse those structural changes. Doctors caution that it can take many weeks or months before patients begin to feel better and see improvements from taking antidepressants. The experience varies from person to person. Many individuals try different kinds of antidepressants to find what works well for them and what doesn't produce unpleasant side effects, such as dizziness, nausea, sexual dysfunction, or fatigue. For one in three people, antidepressants don't provide any relief.

As with all medications, you should explore the benefits and risks of using antidepressants in consultation with your doctor. And remember that other non-medication options exist that may relieve your symptoms. One such treatment is called transcranial magnetic stimulation (TMS). It is a noninvasive, non-drug treatment that uses magnetic pulses to stimulate nerve cells to improve the brain signaling that helps regulate moods. All in all, antidepressants have helped many people live more fulfilling lives. But if they don't provide relief for you, or if their side effects prove too detrimental, talk with your doctor to see if TMS therapy might be right for you.