How Do Antidepressants Work? How Fast They Start Working?

Last Updated: June 10, 2020

Authored by Sharon Levy, MD, MPH

When it comes to what antidepressants do, most people only understand that they treat depression. There tends to be a knowledge gap when it comes to how antidepressants work. For this, patients must know the antidepressant mechanism of action.

How Do Antidepressants Work?

When people are depressed, they naturally look for solutions, often without stopping to question how they work. It is common for a patient to look into how to get antidepressants without considering the numerous ways the medications can impact the body. How antidepressants work comes down to their mechanism of action or MOA.

There are many types of depression drugs, and each type has a slightly different mechanism of action. However, all of them ultimately function by increasing the levels of so-called feel-good chemicals in the brain. Sometimes, patients end up trying many types of antidepressants before finding one that seems to treat their condition.

how fast antidepressants work

How Long Does It Take For Antidepressants To Work?

When patients start taking depression drugs, they expect the mechanism of action to work quickly. This is because most medications on the market show effects instantly, or within just a few days. Depression drugs are different. While atypical antidepressant side effects and negative symptoms of use from other depression medications can show up quickly, the positive effects of the medications are rarely felt sooner than six weeks after beginning a medication regimen.

Can Antidepressants Work Immediately?

It takes time for medications to alter brain chemistry in a noticeable and sustainable manner. Given that this is what antidepressants do, it means that they do not work immediately. However, that does not mean that a user won’t feel like they do.

Why Do Antidepressants Take So Long To Work?

Shortly after the first dose is taken, it will act on the brain and increase the presence of feel-good chemicals. This makes people wonder why, if there is an immediate physical response to them, do antidepressants not work instantly. In essence, this is a misunderstanding of the drugs.

With this said, some of these medications work faster than others. For example, the names of some SNRI antidepressants are listed as being faster acting, given their mechanism of action can be noticed in as little as two weeks. However, most will take more than a month for the user to experience noticeable results.

What Do Antidepressants Do To The Brain?

The effects of antidepressants on the brain can be divided into two categories: intended effects and side effects.

The intended effects are those related to the feel-good chemicals. Antidepressants work by preventing these chemicals from being reabsorbed too quickly, which results in more of them being present in the brain at any given time. The mechanism of action is designed to change the very chemistry of the brain.

Side effects are wide-ranging. For example, some of the side effects of MAOI antidepressants on the brain include from difficulty concentrating to suicidal thoughts and actions.

Do Antidepressants Permanently Alter Brain Chemistry?

Another common concern is if the drugs permanently alter brain chemistry. Here, the answer gets a bit fuzzy. The truth is that while these medications are widely studied, it is not fully understood how antidepressants work. What is known about the mechanism of action is fairly limited, which makes it hard to attribute lasting effects to the medications alone.

how antidepressants affect brain

Long-term use of antidepressants that increase dopamine has been found to cause alterations in the brain, even after use has stopped. In fact, the body can struggle to produce the dopamine the brain needs to function, resulting in a more profound experience of depression.

There is also a link between antidepressants and estrogen. Both the medications and the hormone are known to increase certain feel-good chemicals in the brain. It is theorized, though not definitively proven, that as antidepressants work, the body sees less need to produce estrogen. As a result, antidepressants and estrogen levels dropping can result in long-term adverse hormonal effects.

What Do Antidepressants Do For Anxiety?

Antidepressant medications are often used in the treatment of anxiety. However, not all types of depression medications work for anxiety disorder treatment. The only class that has been shown to work well for anxiety is SSRIs. The mechanism of action results in faster improvement with anxiety than it does with depression, seeing results in as little as two weeks.

Because these medications are not designed to treat anxiety, there is a concern that side effects are more likely to emerge from treatment. Users should exercise caution when prescribed antidepressants for anxiety.

Why Antidepressants Don’t Work

While they are sometimes presented as a miracle drug, for many who are prescribed them, antidepressants don’t work. As it happens, research indicates that they are not nearly as effective as many have been lead to believe. Studies have found that roughly 40 percent of people with depression will see improvement when given a placebo—no medicine at all. When given an antidepressant, 60 percent of people see an improvement—only 20 percent more than those not given any medication at all.

Why antidepressants don’t work significantly better than a mere placebo is not fully understood. However, for those in that 20 percent who do see effects from the medication, it still has its benefits.

woman whose antidepresants do not work

What To Do When They Don’t Work

When antidepressants don’t work, it is possible that the user simply needs to be switched to other drugs, as it may be that the current ones are not for them. For those who find them effective, oftentimes, it is only for short-term treatment. Once they are not as effective, it may be better to look into alternatives to antidepressants.

If someone is prescribed depression drugs, and they do not work, they will need to end the use of the medications safely. This should never be done alone or cold-turkey.

By consulting with a drug rehabilitation facility or experienced doctor, the user will be able to determine a good tapering schedule and safely get off antidepressants. Drug rehabilitation centers can address all aspects of ending these drugs use by effective treatment to ensure long-standing results.

Page Sources

  1. Cologne, Germany: Institute for Quality and Efficiency in Health Care (IQWiG). Depression: How effective are antidepressants? 2006.
  2. Kaneko F, Kawahara Y, Kishikawa Y, et al. Long-Term Citalopram Treatment Alters the Stress Responses of the Cortical Dopamine and Noradrenaline Systems: the Role of Cortical 5-HT1A Receptors. The International Journal of Neuropsychopharmacology. 2016; 19(8): pyw026. doi:10.1093/ijnp/pyw026.

Published on: October 15th, 2019

Updated on: June 10th, 2020

About Author

Sharon Levy, MD, MPH

After successful graduation from Boston University, MA, Sharon gained a Master’s degree in Public Health. Since then, Sharon devoted herself entirely to the medical niche. Sharon Levy is also a certified addiction recovery coach.


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