Antidepressant medications can help relieve symptoms of depression, social anxiety disorder, anxiety disorders, seasonal affective disorder, dysthymia (persistent depressive disorder), and mild chronic depression, as well as other conditions such as obsessive-compulsive disorder or post-traumatic stress disorder. But how do these medications work? What effects do they have?
Anti-depression medications aim to correct chemical imbalances in the brain that are thought to be responsible for changes in mood and behavior. First developed in the 1950s, their use has become increasingly common over the past 20 years.
Are antidepressants effective?
It should be noted that antidepressants do not take effect as soon as they are started, but in many cases, it takes several weeks for the person to begin to notice their effects .
Research suggests that anti-depression medications may be helpful for people with moderate to severe depression. Studies have shown that they have a positive effect greater than placebo in people with depression. They are generally not recommended for mild depression unless other alternatives, such as therapy, have failed.
The Royal College of Psychiatrists estimates that 50-65% of people treated with an anti-depression drug will see improvement, compared with 25-30% of people taking a placebo.
What do antidepressants do?
If we’re being strict, experts aren’t entirely sure how some antidepressants work—most antidepressant drugs work by increasing the levels of specific neurotransmitters in the brain. Typically, they prevent these neurotransmitters from being reuptaken from the intersynaptic space.
This means that they remain in the synapses longer, causing more activity, thereby ‘compensating’ for the reduced levels. Antidepressants thus cause the remaining neurotransmitters to work more effectively, so that overall activity is, so to speak, more ‘normal’.
However, this doesn’t explain how antidepressants end up alleviating depressive symptoms. Neurotransmitters are like the building blocks for something much more complex. They’re the equivalent of numbers in figures or letters in language. So increasing neurotransmitter levels throughout the brain doesn’t say anything specific.
On the one hand, anti-depression medications increase neurotransmitter activity fairly immediately, but the therapeutic effects often take weeks to become noticeable on a subjective level.
How Different Depression Medications Work
Many researchers believe that the benefits of antidepressants stem from how they affect certain brain circuits by modifying the levels of neurotransmitters. These include serotonin, dopamine, and norepinephrine.
Different types of anti-depression medications appear to affect the level of these neurotransmitters in different ways. Let’s look at how they do this below.
Reuptake inhibitors
Some of the most commonly prescribed antidepressants are called reuptake inhibitors. Reuptake is the process in which neurotransmitters are naturally reabsorbed into nerve cells in the brain after they are released to send messages between nerve cells.
A reuptake inhibitor prevents this from happening. Instead of being reabsorbed, the neurotransmitter remains, at least temporarily, in the gap between nerves, called the intersynaptic space.
In theory, the benefit of these drugs is to keep levels of a certain neurotransmitter high, which could improve communication between nerve cells, strengthening the brain circuits that regulate mood.
There are different types of reuptake inhibitors depending on the different neurotransmitters they target, including:
- Selective serotonin reuptake inhibitors.
- Serotonin and norepinephrine reuptake inhibitors.
- Norepinephrine and dopamine reuptake inhibitors.
Tetracyclics
Tetracyclines are another class of antidepressants that, while they affect neurotransmitters, do not prevent reuptake in the same way. Instead, they appear to prevent neurotransmitters from binding to specific receptors on nerves. Because norepinephrine and serotonin do not bind to receptors, they appear to build up between nerve cells. As a result, neurotransmitter levels increase.
These depression medications appear to work in two ways. First, they prevent the reuptake of serotonin. Second, they prevent serotonin particles released into a synapse from binding to certain unwanted receptors and instead redirect them to other receptors that can help nerve cells function better in neural circuits associated with mood.
Tricyclics and MAOIs
These drugs were among the first to be used for depression. Although they are effective, they can have significant side effects, which are especially serious in the case of an overdose. Today, many doctors only turn to these drugs when newer, better-tolerated medications have not been effective.
However, tricyclics and MAOIs (monoamine oxidase inhibitors) can sometimes be very helpful for people with treatment-resistant depression or certain forms of depression (such as depression that coexists with high levels of anxiety).
Tricyclic antidepressants also prevent the reuptake of neurotransmitters, but they do so in a non-selective manner, acting on serotonin, norepinephrine, and dopamine, among others, at the same time. Although these drugs are effective in treating depression, they are currently being replaced by more specific drugs.
Monoamine oxidase inhibitors (MAOIs) block the effects of monoamine oxidase, a natural enzyme that breaks down serotonin, epinephrine, and dopamine. As a result, levels of these neurotransmitters may increase.
The downside is that MAOIs also prevent the body’s ability to break down other drugs metabolized by this enzyme, which increases the risk of high blood pressure, as well as levels of an amino acid called tyrosine found in certain foods, such as aged meats and cheeses.
MAOIs should also not be combined with other medications that can increase serotonin (such as certain migraine medications or other antidepressants), as this may cause an excessive buildup of serotonin, called ‘serotonin syndrome’, which could be life-threatening.
Final comments
Much of what is thought about antidepressants today is still speculative. It is not known whether low levels of serotonin or other neurotransmitters cause depression or whether raising those levels will resolve it. Perhaps we do not yet know enough about brain chemistry to say what is balanced or unbalanced.
It’s possible that antidepressants have other, unknown effects, and that their benefits may have less to do with neurotransmitter levels than with other effects, such as regulating genes that control nerve cell growth and function.
This may not sound very reassuring. However, while experts don’t have all the answers about how antidepressants work, we do know that they can work. Many studies have established that antidepressants can help many people feel better, and that’s what’s important.