How Long Does It Take for Prozac to Work?

Published on: 22 May 2023
Clinically Reviewed by Karmen Smith LCSW, DD

Prozac, and the generic form Fluoxetine, is a selective serotonin reuptake inhibitor (SSRI medication) used to treat symptoms related to depression and other mental health conditions like anxiety. Prozac works by increasing one’s serotonin level in the brain, improving mood and reducing depressive symptoms. Studies show that while Prozac can effectively treat symptoms of severe depression and other mental health conditions, for most people it doesn’t work right away. If you’re thinking about taking Prozac, it’s important that you understand the effects aren’t going to be immediate.

So, how long does Prozac take to work? The length of time it takes for Prozac to work can vary, but most people begin feeling the beneficial effects within two weeks or so. However, this timeframe can vary depending on individual factors, like age and body weight. As a result, some people may experience relief from their symptoms quickly, while others need more time before feeling any improvement in their condition.

Keep reading to learn what to expect if you start taking Prozac. We’re answering the question: how long does it take for Prozac to start working and covering what you can expect week to week, how to know if it’s not working, and more. 

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Can Prozac Work Immediately?

If you want to know how long Prozac takes to work and are wondering if it works right away, the short answer is no — Prozac generally doesn’t work right away. Most people need to take it for several weeks before feeling better. That said, some people may experience relief from their symptoms within a few days (or even hours) after taking the first dose.

No matter what dosage you’re on, there’s no guarantee you’ll experience immediate relief from your anxiety or depression symptoms. Many people don’t notice changes until several weeks into treatment with Prozac or any other SSRI antidepressant medication. This doesn’t mean that the drug isn’t working. It might just mean your body needs more time to adjust and respond positively to the drug therapy regimen your doctor or healthcare provider prescribed.

How quickly does Prozac work for anxiety?

How quickly Prozac starts working to treat anxiety depends on several factors, such as age, medical history, and severity of your condition. Typically, younger adults respond more rapidly than older adults when starting an antidepressant like Prozac. Additionally, people with milder cases of depression or anxiety might see results sooner than those with more severe cases.

What Does It Feel Like When Prozac Starts Working?

When an antidepressant like Prozac begins working effectively, many people report feeling calmer and less anxious than they were before starting treatment. 

Other common feelings associated with Prozac include: 

  • Increased energy levels
  • Improved sleep patterns
  • Decreased irritability
  • Better concentration
  • Improved self-esteem
  • Reduced stress levels
  • Fewer negative thoughts in general 

Some people report experiencing greater joy in life when using antidepressants over long periods.

Week by week

How long for Prozac to work? For most people, it takes anywhere from 1 to 4 weeks for Prozac to begin showing its effects. The time frame depends on various factors, like individual metabolism and response, dosage strength, and other medications being taken concurrently.

  • Week 1: During the first week of taking Prozac, most people don’t experience noticeable changes in their mood or behavior. Some people, though, may feel an increase in energy levels or a decrease in appetite due to the drug’s action on serotonin receptors in the brain.
  • Week 2: By this point, some people may notice subtle improvements in their overall outlook and emotional state. This could include feeling less anxious or depressed than they were before they started taking Prozac. They also might have more motivation and focus when completing tasks throughout the day.
  • Week 3: After 3 weeks of treatment with Prozac, most people start to generally feel better. They often find that their symptoms aren’t as severe, and their daily functioning has improved significantly.
  • Week 4: At this stage, many individuals will see even more significant improvements in their mental health. They might have increased feelings of well-being, reduced anxiety levels, and fewer depressive thoughts than before. Those taking higher doses might be able to lower their dosage slightly without experiencing severe side effects of Prozac.

Factors that Affect the Onset of Action for Prozac

Prozac’s onset can vary from person to person and depends on several factors, including:

  • Body weight: People who are overweight or obese may take longer to experience the positive effects of Prozac when compared to those with average body weight. This is because fat cells absorb more medication than lean muscle tissue. It’s important to note, too, that while not as common, Prozac weight gain can occur.
  • Metabolism: Metabolism plays a vital role in how quickly medications like Prozac start working. Those with slower metabolisms may take longer to feel the effects since their bodies process drugs differently.
  • Age: Age is another factor in the onset of action for Prozac. Older adults may require higher doses due to their slower metabolism, which can lead to a more extended period before any changes in mood or behavior are noticed.
  • Dosage: The dosage of Prozac is another important factor in onset of action. If too low a dose is taken, symptom relief can be delayed. Conversely, taking too high an amount might lead to adverse side effects — like nausea, dizziness, insomnia, and agitation — further delaying symptom relief.  

“There are many different things that can counteract the effects of Prozac, but the most popular include drugs and/or alcohol (including many prescription drugs), caffeine, processed meat, some cheeses, chocolate, avocados, and BMI, stress, and committedness to changing dysfunctional thought patterns, beliefs, and perspectives.”

Talkspace therapist Meaghan Rice, PsyD, LPC

What to Do When Prozac is Not Working

If you’ve been taking Prozac and it isn’t working as well as you hoped, here are some steps you can take.

Talk to your doctor

The first step should always be talking to your doctor or a medical professional about your experience and acquiring proper medical advice. They may suggest increasing the dosage or trying another medication altogether. You should discuss any side effects or concerns you have, so they can make an informed decision about what would work best for you.

Try other medications

If increasing the dosage doesn’t work, your doctor may recommend switching to another type of antidepressant or even trying other forms of treatment, like psychotherapy or lifestyle changes. Make sure to ask questions and get all the information necessary before making any decisions regarding changing psychiatrist prescribed medications or treatments.

Look into natural remedies

In addition to traditional medical treatments, natural remedies could help alleviate some of your symptoms associated with depression and anxiety disorders. These include self care like yoga, meditation, acupuncture, and some herbal supplements, which have been known to reduce stress levels and improve moods. Always consult your physician before starting any natural remedies for depression or anxiety.

Get Personalized Mental Health Treatment with Talkspace

Are you looking for a way to get personalized mental health treatment? Are you wondering how long until Prozac works to improve your symptoms? Talking to a mental health professional can offer all the answers you’re looking for. Talkspace is an online psychiatry and therapy platform that provides users access to licensed therapists and psychiatrists and can help you get Prozac online. With Talkspace, you can connect with your therapist or psychiatrist anytime, anywhere — from the comfort of your home.


  1. Rossi A, Barraco A, Donda P. Annals of General Hospital Psychiatry. 2004;3(1):2. doi:10.1186/1475-2832-3-2. Accessed February 8, 2023. 
  2. Selective serotonin reuptake inhibitor. Selective Serotonin Reuptake Inhibitor – an overview | ScienceDirect Topics. Accessed February 8, 2023. 

Talkspace articles are written by experienced mental health-wellness contributors; they are grounded in scientific research and evidence-based practices. Articles are extensively reviewed by our team of clinical experts (therapists and psychiatrists of various specialties) to ensure content is accurate and on par with current industry standards.

Our goal at Talkspace is to provide the most up-to-date, valuable, and objective information on mental health-related topics in order to help readers make informed decisions.

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