How Long Prozac Stays in Your System: What That Means for Side Effects and More

Prozac (fluoxetine) is a popular medication for treating depression, anxiety, and other mental health conditions. It belongs to a class of medications called selective serotonin reuptake inhibitors (SSRIs). Compared to other SSRIs, Prozac lasts the longest in your body.

Prozac’s long-lasting effects may be one of the reasons you would be prescribed it in the first place. But what does that mean for after you’ve stopped taking it? 

Because Prozac can linger in your body for weeks after your last dose, it tends to have a lower risk of withdrawal symptoms. But this can also mean that the side effects take longer to fully resolve. And interactions can still be an issue for weeks, too. 

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How long does Prozac stay in your system?

After you take a dose of Prozac, it’s removed from the body very slowly. And if you’ve been taking Prozac for a while, it takes about 4 to 6 days for your body to get rid of just half of it. 

For most people, it takes about 1 month for fluoxetine (the main ingredient in Prozac) to be completely eliminated from the body after the final dose. However, a portion of the medication is also converted into an active chemical called norfluoxetine, which can hang around in the body for even longer. 

Keep in mind: The time it takes a medication to fully leave the body will be different for everyone. For example, people with liver problems may clear Prozac more slowly. And how long you’ve been taking Prozac can make a difference, too.

What happens when you stop taking Prozac?

There are several things to keep in mind if you’ve decided to stop taking Prozac. Most importantly, your healthcare provider should be included in this decision. They can help you develop a plan for how to stop taking it safely and manage side effects, interactions, and more.

Side effects

Common Prozac side effects include trouble sleeping, nausea, and headache. But sexual problems and tremors are also possible. 

Some Prozac side effects get better over time, while others may persist as long as you’re taking the medication. If you’ve been instructed to stop taking Prozac due to side effects, keep in mind they may not fully resolve right away.

Sometimes, certain side effects get worse after a person stops taking Prozac. For some people, this might be due to antidepressant discontinuation syndrome. More on that next.

Discontinuation syndrome

Antidepressant discontinuation syndrome can happen to some people who suddenly stop taking antidepressants or have their dose lowered too quickly. The medications that can cause this effect include SSRIs, tricyclic antidepressants (TCAs), and monoamine oxidase inhibitors (MAOIs), among others.

In most cases, discontinuation syndrome isn’t life-threatening. But it may cause bothersome withdrawal symptoms for a week or two, and sometimes longer. Examples include flu-like symptoms, headache, and nausea. And trouble sleeping and restlessness are also possible.

Not all SSRIs carry the same risk for discontinuation syndrome. It’s more common with SSRIs that leave the body faster, like Paxil (paroxetine). Since Prozac takes longer to leave the body, it has a lower risk of discontinuation syndrome. 

If you need to stop taking Prozac, talk to your healthcare provider about how to stop treatment safely. You might be able to stop taking Prozac right away, or your provider may recommend slowly reducing your dose before stopping completely.

Keep in mind: It can be difficult to tell whether you’re experiencing withdrawal symptoms or your original symptoms are coming back. Tell your healthcare provider if you have any symptoms that are severe, don’t go away, or get worse.

Interactions

There are many medications that are broken down by the same enzymes (proteins) as Prozac. And even after you’ve stopped taking Prozac, it can still potentially interact with these medications, as long as it’s still in your system. Some interactions are more serious, while others can be managed with monitoring. 

Below are a few examples of the types of medications that can interact with Prozac:

• Medications that raise serotonin levels: Prozac makes more serotonin available in your brain. Taking it with other medications that affect serotonin can lead to a dangerous condition called serotonin syndrome. Examples of these medications are MAOIs, TCAs, and serotonin and norepinephrine reuptake inhibitors (SNRIs).

• Medications that increase your risk of bleeding: Prozac can increase your risk of bleeding. This risk is higher when Prozac is combined with other medications that have the same side effect. Examples include nonsteroidal anti-inflammatory drugs (NSAIDs) and blood thinners, among others. 

• Medications that affect heart rhythm: Although the risk appears to be low, Prozac can lengthen the time between heartbeats. This can result in life-threatening arrhythmias. Taking Prozac with other medications that may have a similar effect can increase this risk. Examples include ziprasidone (Geodon), erythromycin (Ery-Tab), and amiodarone (Pacerone).

So when is it safe to take these medications after stopping treatment with Prozac? The manufacturers don’t have specific recommendations for all of them. But it is recommended to wait 5 weeks after stopping Prozac before starting some of the more high-risk medications, like MAOIs.

Before you start taking a new medication, tell your healthcare provider if you’ve recently taken Prozac. They can check for interactions and help you figure out when it’s safe to start taking the new medication.

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Written by:

Kristianne Hannemann, PharmD

Kristianne Hannemann, PharmD, is a licensed pharmacist in California. She has been a retail pharmacy manager and staff pharmacist for over 7 years and has contributed drug information content to different health companies.

Edited by:

Alyssa Billingsley, PharmD

Alyssa Billingsley, PharmD, is the director of pharmacy content for GoodRx. She has over a decade of experience as a pharmacist and has worked in clinical, academic, and administrative roles.

Reviewed by:

Sarah Gupta, MD

Sarah Gupta, MD, is a licensed physician with a special interest in mental health, sex and gender, eating disorders, and the human microbiome. She is currently board certified by the American Board of Psychiatry and Neurology.

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