How Long Does Prozac Stay in Your System? Half-Life and More

By Alicia Wooldridge, MD
Medically reviewed checkmarkMedically reviewed
February 24, 2022

Fluoxetine (Prozac) is a prescription medication used to treat depression, obsessive compulsive disorder (OCD), and other mental health conditions.

Like most antidepressants, Prozac can help to alleviate symptoms of depression and anxiety in many people, but it isn’t right for everyone. 

After starting Prozac, you may experience some unwanted side effects or find that the medication isn’t working to resolve your symptoms.

In those cases, you and your psychiatrist (or another licensed healthcare provider) may decide that switching to another antidepressant medication or stopping Prozac altogether may be best for you. 

When stopping the medication, you may wonder how long the medication will stay in your system, especially if you’re scheduled to take a blood, urine, or drug test. In this article, I’ll describe how Prozac works, how long the medication can stay in your system after discontinuing use, and whether drug tests can detect Prozac in your body.

What is Prozac?

Prozac is one of the most commonly prescribed medications in the United States. It’s a type of antidepressant medication called a selective serotonin reuptake inhibitor (SSRI).

SSRIs work by increasing the levels of serotonin, a neurotransmitter, in your brain.

Serotonin can help your body perform many functions, including learning and memory, but it can also help to stabilize mood, emotions, and improve sleep.

A medical professional may prescribe Prozac for several conditions, including:

  • Major depressive disorder (MDD)
  • Obsessive compulsive disorder (OCD)
  • Bulimia nervosa
  • Anxiety – including panic disorder
  • Premenstrual dysphoric disorder (PMDD)

When taking a prescription antidepressant like Prozac, it’s essential that you take the medication at the same time every day and only as directed by your provider. 

It may take up to six or eight weeks for Prozac to start taking effect and you may experience some side effects during that time period, including:

  • Insomnia or strange dreams
  • Headache
  • Dizziness
  • Vision changes
  • Tremors or shaking
  • Worsened feelings of anxiety or nervousness
  • Fatigue
  • Pain
  • Weakness
  • Indigestion
  • Dry mouth
  • Sweating or hot flashes
  • Changes in appetite
  • Changes in weight (weight loss is especially common in children)
  • Stuffy nose or other flu-like symptoms
  • Sexual side effects, including decreased sex drive, impotence, or trouble reaching orgasm

In most cases, these side effects resolve on their own as your body adjusts to the medication.

But if any of these side effects persist, you should reach out to your provider to see if an adjustment in dosage or medication type is needed.

To avoid withdrawal symptoms, you should never stop taking Prozac suddenly or without the guidance of a healthcare professional.

If you’re considering stopping or switching medication, talk to your provider about the right tapering off schedule for you and your dosage.

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Prozac Half-Life

The half-life of Prozac will vary depending on how long you’ve been taking the medication:

  • 1-3 days after acute administration
  • 4-6 days after chronic administration

Because Prozac is a longer-acting medication than some short-acting antidepressants (including Zoloft and Paxil), it will take longer to leave the body completely.

Specifically, it can take around 25 days or more for Prozac to leave your system.

How Long Prozac Stays in Your Blood

Once inside your body, Prozac is absorbed by the gut and then metabolized in the liver, after which it’s metabolites are circulated in your bloodstream.

For this reason, it can take some time for Prozac to leave your blood, even after stopping the medication.

Blood tests are not often used to detect the presence of Prozac in your system.

However, because blood tests are one of the most accurate test types, they can identify the medication in your system for around three months after discontinuing use. 

How Long Prozac Stays in Your Urine

Similarly, urine tests are not typically used to screen for the Prozac.

But it’s possible for Prozac to stay in the urine for as long as it can stay in the blood: around three months.   

Top Factors that Affect Prozac Timeline in Your Body

Working with a provider is essential to stopping Prozac safely.

However, how long Prozac stays in your system can vary depending on several factors, including your age and health history. 

When following a tapering off schedule recommended by your provider, the amount of Prozac you take is gradually reduced.

Once you reach the end of your tapering off schedule, it may still take some time for the medication to leave your system completely. 

There are several factors that can impact how long Prozac stays in your system, including:

  • Age: Older individuals usually take longer to metabolize Prozac.
  • Medication history: How long you’ve been taking Prozac and whether or not you take other medications can impact how long Prozac stays in your system. Generally, the longer you’ve been taking Prozac the longer its half-life in your system.
  • Metabolism and genetic factors: The slower your metabolism, the longer it will take for Prozac to leave your system.
  • Liver and kidney function: Liver and kidney diseases impact the plasma concentration and dose requirements for nearly all medications, including antidepressants like Prozac. Because Prozac is primarily eliminated in the urine, liver and kidney impairment is associated with a longer Prozac half-life

Importantly, once you’ve finished the medication and Prozac is out of your system, symptoms of your condition (including depression or anxiety) may return.

However, one Harvard Medical School study shows that tapering off of the medication gradually reduces the risk that symptoms of depression will recur.

Will Prozac Show Up on Drug Tests?

Most standard drug tests are not designed to identify the presence of antidepressant medications like Prozac in the body.

However, there are some studies that show that medications like Prozac can cause a false-positive in LSD and amphetamine screening tests. 

If you are planning to take a drug test while on Prozac or within three months of stopping Prozac, consider speaking to the personnel in charge of the test about the possibility of a false-positive caused by your prescription medication.

Getting Prozac Out of the System

There’s no shame in reaching out to a provider for medical advice if Prozac isn’t working for you.

However, it’s important to remember that getting Prozac out of your system safely involves gradually tapering off of the medication.

Otherwise, stopping Prozac abruptly can cause withdrawal symptoms, including:

  • Irritability
  • Nausea
  • Dizziness
  • Vomiting
  • Nightmares
  • Headache
  • Paresthesias (prickling or tingling sensation on the skin)

When stopping the medication and getting Prozac out of your system, you may decide to reach out to a friend or family member for support.

Keeping a journal or diary of any new symptoms during this period may also be a good idea.

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When to See a Doctor

If Prozac isn’t working to resolve your symptoms or if you’re experiencing unwanted side effects (including suicidal thoughts), reach out to your provider or a healthcare professional immediately to discuss your options. 

It’s also important to keep an eye out for any of the rare but serious side effects, including:

  • Severe dizziness
  • Hives, or a red or purple rash with blistering or peeling
  • Itching or swelling, particularly of the mouth, face, or throat
  • Difficulty breathing
  • Seizure
  • Abnormal bleeding or bruising

Additionally, speak to your provider as soon as possible if you experience any of the following signs of an overdose:

  • Unsteadiness
  • Confusion
  • Unresponsiveness
  • Nervousness
  • Uncontrollable shaking
  • Rapid, pounding, or irregular heartbeat
  • Hallucinations
  • Fainting

How K Health Can Help

Did you know

Think you might need a prescription for Prozac (fluoxetine)?

K Health has clinicians standing by 24/7 to evaluate your symptoms and determine if Prozac is right for you.

Get started with our free assessment, which will tell you in minutes if treatment could be a good fit. If yes, we’ll connect you right to a clinician who can prescribe medication and have it shipped right to your door.

K Health articles are all written and reviewed by MDs, PhDs, NPs, or PharmDs and are for informational purposes only. This information does not constitute and should not be relied on for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment.

Alicia Wooldridge, MD

Dr. Alicia Wooldridge is a board certified Family Medicine physician with over a decade of experience.

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