How long does it take for Prozac (fluoxetine) to work?

How long does it take for Prozac (fluoxetine) to work?

It takes at least four weeks for Prozac to work for depression and OCD but some people may feel the effects as soon as two weeks after taking it regularly.

Reviewed by:
Austin Lin, MD
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May 19, 2024
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Key takeaways

Prozac (fluoxetine) is an antidepressant that’s regularly used to treat depression, OCD, and a variety of anxiety disorders. If you’ve been prescribed Prozac, you’re probably wondering how long it will take to start working, and when exactly you can expect to feel better. Like many medications, how long it takes to work depends on a few different factors, including why you’re taking it. In general though, you should start to notice small changes over the course of the first several weeks.

In this article, we’ll cover how long it takes Prozac to work for different mental health conditions, what it feels like when it starts working, and what to look out for.

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How long does Prozac take to work?

Prozac is the brand name for the SSRI (selective serotonin reuptake inhibitor) fluoxetine. The amount of time it takes to work varies on the medical condition you’re taking it for and your symptoms, but typically it takes a few weeks to feel the full benefits.  

  • Major depressive disorder (MDD): It can take between 4 to 8 weeks to feel the full effect of the medication. But people in some clinical trials have reported a lessening of their symptoms of depression after just 2 weeks.  
  • Obsessive-compulsive disorder (OCD): It can take 4 to 6 weeks for Prozac to work, though it may take up to 12 weeks for some people. OCD symptoms also tend to respond to higher doses of SSRIs than lower doses, so this can add to the time.
  • Bulimia nervosa: Some studies have shown that people notice relief from their symptoms within 3 weeks of taking the medication.  

Your doctor will likely start you on a low dose of Prozac, adjusting it over time to reach the right dose for you. Remember, never increase your dose without talking to your doctor first.  

What does Prozac feel like when it starts working?

Research indicates that if the dose of Prozac that you’re taking is effective for your symptoms, you may notice signs that it’s working within the first week or two. But if you haven’t noticed any differences after taking Prozac for 4-6 weeks, you most likely won’t respond to the medication at this dose, or Prozac might not be right for you.

Here are eight common signs that Prozac is working:  

  • You find yourself enjoying life more fully.
  • You feel less depressed or anxious
  • You have more energy.
  • You’re sleeping better.
  • You have a more regular appetite.
  • You have an easier time doing your normal daily activities.
  • You’re less preoccupied by your mental health symptoms.
  • You have a reduced desire to binge eat or throw up (if you’re taking it for an eating disorder like bulimia).

Side effects of Prozac

Another way you might know medication is working is that you’ll start to feel some of its common side effects. For Prozac, these include nausea, drowsiness, dry mouth, and sexual side effects, including sexual dysfunction.  

When is the best time of day to take Prozac?

Many people find it beneficial to take Prozac in the morning because it can interfere with your sleep. However, some patients find Prozac to be sedating. Talk to your psychiatrist about sleep interruptions from Prozac in order so they can help determine the best course of action to take next.  

No matter when you decide to take it, try to take it at the same time each day. This can help you feel Prozac’s effects more consistently.  

What should you look out for when taking Prozac?

During the first three weeks of taking Prozac, you may  notice some mild common side effects—like trouble sleeping, agitation, headache, stomach upset, or decreased sexual drive—though these usually will go away within a week or two.

If you experience a lot of discomfort—including increased suicidal thoughts—or find the effects don’t get better over time, talk to your doctor. They may decide to decrease your dose or have you try another medication.  

When you begin taking any new medication, it’s important to keep an eye on your symptoms and how you’re feeling. Consider keeping a journal to take notes, and share it with your doctor. This way they can help make sure the medication is working the way it’s supposed to.

And if Prozac does help you feel better, don’t stop taking it on your own. Stopping medication suddenly can have negative effects or “withdrawal symptoms,” so let your doctor know first if you want to stop and they can help come up with a plan for you to go off Prozac safely and effectively.  


Here's what else to know about Prozac's timing and effects.

How does Prozac work?

Prozac works by increasing the levels of serotonin, a neurotransmitter in the brain that helps regulate mood, in order to alleviate symptoms of depression, anxiety, and other related conditions.

Does Prozac work immediately?

The effects of Prozac may not be immediately noticeable, and it typically takes several weeks for the medication to reach its full therapeutic effect. How long pindividuals may start experiencing positive changes in their symptoms within the first few weeks of treatment.

What are other treatment options for anxiety?

Alternatives to Prozac include other SSRIs like Zoloft (sertraline) and Paxil (paroxetine), SNRIs like Effexor (venlafaxine), MAOIs (monoamine oxidase inhibitors), TCAs (tricyclic antidepressants), and atypical antidepressants.

The information in this article is for education and informational purposes only and should never be substituted for medical advice, diagnoses, or treatment. If you or someone you know may be in danger, call 911 or the National Suicide and Crisis Lifeline at 988 right away.

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What's the difference between a therapist and psychiatrist?

Psychiatrists are doctors who have specialized training in diagnosing and treating complex mental health conditions through medication management. If you are experiencing symptoms of a mental health condition such as depression, anxiety, bipolar disorder, PTSD, or similar, a psychiatrist may be a good place to start.  

Other signs that you should see a psychiatrist include:  

  • Your primary care doctor or another doctor thinks you may benefit from the services of a psychiatrist and provides a referral    
  • You are interested in taking medication to treat a mental health condition  
  • Your symptoms are severe enough to regularly interfere with your everyday life

The term “therapist” can apply to a range of professionals including social workers, mental health counselors, psychologists, professional counselors, marriage and family therapists, and psychoanalysts. Working with a therapist generally involves regular talk therapy sessions where you discuss your feelings, problem-solving strategies, and coping mechanisms to help with your condition.

How does Talkiatry compare to face-to-face treatment?

For most patients, Talkiatry treatment is just as effective as in-person psychiatry (American Psychiatric Association, 2021), and much more convenient. That said, we don’t currently provide treatment for schizophrenia, primary eating disorder treatment, or Medication Assisted Treatment for substance use disorders.

Who can prescribe medication?

All our psychiatrists (and all psychiatrists in general) are medical doctors with additional training in mental health. They can prescribe any medication they think can help their patients. In order to find out which medications might be appropriate, they need to conduct a full evaluation. At Talkiatry, first visits are generally scheduled for 60 minutes or more to give your psychiatrist time to learn about you, work on a treatment plan, and discuss any medications that might be included.

Austin Lin, MD

Dr. Austin Lin is a double board-certified adult and addiction psychiatrist who has been in practice for over 9 years. At the center of Dr. Lin’s clinical approach is a strong emphasis on establishing trust and using a collaborative approach to help patients develop an individualized and cohesive plan so that they are able to achieve their goals.

Dr. Lin's practice focuses on medication management. Typically, he offers this in conjunction with supportive therapy, motivational interviewing, and/or cognitive behavioral therapy in 30-minute follow-up visits. Occasionally, Dr. Lin may recommend that additional therapy is needed and ask that you bring a therapist into your care team in order to provide the best outcome.

Dr. Lin received his medical degree from St. George’s University School of Medicine. He went on to complete his residency in psychiatry at Harvard South Shore, an affiliate of Harvard Medical School, where he served as Chief Resident and earned his 360° Professionalism award. He then had additional training in Addiction Psychiatry through his fellowship at the University of Texas Southwestern Medical Center. After completing training, Dr. Lin has worked as an Addiction Psychiatrist and Director of Adult Services in the Trauma and Resilience Center (TRC) at the University of Texas Health Science Center at Houston (UTHealth). He specialized in treating patients with a history of depression, anxiety, trauma, and substance use disorders.

Dr. Lin has held an academic appointment at UTHealth, and he has spent his professional career supervising and teaching medical students and psychiatry residents.

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