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Fluoxetine, better known by the trade name Prozac, is one of the most popular antidepressants in the United States. In fact, in 2017 medical providers issued 25,619,277 prescriptions for fluoxetine hydrochloride. A selective serotonin reuptake inhibitor (SSRI), this medication can help treat conditions like depression and obsessive-compulsive disorder (OCD). Given how popular this drug is, it pays to know a little more about it, including how long Prozac stays in your system.

Basic Information

The FDA and PharmGKB state the following information regarding Prozac half-life:

  • Slow elimination half-life: 1 to 3 days after acute administration; 4 to 6 days after chronic administration
  • Mean terminal half-life: 8.6 days after single dose; 9.3 days after multiple doses
  • “Steady-state levels” after prolonged administration: 4 to 5 weeks
  • Brain-to-plasma ratio: 2.6:1


What is the half-life of Prozac?

The average half-life of Prozac is about 2 to 4 days. It generally takes around 2 to 4 weeks for Prozac to have an antidepressant effect, according to a 2020 study.

How long does Prozac stay in your system?

It takes about 25 days for Prozac to completely exit the body, according to Harvard Health.

Will antidepressants show up on a drug test?

Someone expecting a routine drug screening may wonder if their prescription medications will cause them to fail these tests. Fortunately, most drug screenings do not check SSRIs, the class of drugs to which Prozac belongs. That said, sometimes antidepressants can cause false-positive results on certain drug screenings. In fact, some research reports that fluoxetine has resulted in false-positive results for LSD screenings and amphetamines.

Disclaimer: this article does not constitute or replace medical advice. If you have an emergency or a serious medical question, please contact a medical professional or call 911 immediately. To see our full medical disclaimer, visit our Terms of Use page.

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