Prozac Side Effects: What's Common and How Long It Lasts
The most common Prozac side effects are nausea, trouble sleeping, nervousness and sleepiness, and many ease in the first weeks.
By withClaro Editorial · 2026-11-02 · 4 min read
Clinical section reviewed by Dr. Jason Tan , Consultant Psychiatrist, on October 27, 2026.
Key takeaways In the FDA depression trials, the most common Prozac side effects were nausea, insomnia, nervousness, sleepiness and anxiety. In 100 r/prozac threads, anxiety or restlessness was the side effect people named most often, followed by tiredness and nausea. Some side effects ease within weeks. On r/prozac more people said theirs were still going than eased, but people who are still in it are the ones who post. Call your prescriber the same day about new thoughts of self-harm, signs of serotonin syndrome or unusual bleeding; the suicide risk warning applies most to people 24 and younger. On this page
What are the most common side effects of Prozac? Which side effects people on r/prozac named How long do Prozac side effects last? Which Prozac side effects are serious? What helps with Prozac side effects? What should you tell your prescriber about Prozac side effects? The most common Prozac (fluoxetine) side effects are nausea, trouble sleeping, nervousness, anxiety and sleepiness. They usually show up in the first days or weeks, before any change in mood: fluoxetine acts from the first dose, while the brain takes weeks to respond, so early side effects don't mean it isn't working.
What are the most common side effects of Prozac?
Nausea leads: 21% on Prozac against 9% on placebo, then insomnia, 16% against 9%, and nervousness, 14% against 9%. These come from the label's depression trials, with 1,728 people on Prozac and 975 on placebo, since most people take it for depression. The side effects seen most often, compared with placebo, were:
Side effect Prozac Placebo Nausea 21% 9% Insomnia 16% 9% Nervousness 14% 9% Sleepiness 13% 6% Anxiety 12% 7% Diarrhea 12% 8% Decreased appetite 11% 2% Tremor 10% 3% Weakness or low energy 9% 5% Sweating 8% 3%
Side effects differ by condition. Insomnia was 28% against 22% on placebo in the OCD trials, and 33% against 13% in the bulimia trials. Across all four conditions in the label, headache was common, at 21%, but almost as common on placebo, at 19%.
Which side effects people on r/prozac named
We read 100 recent threads about side effects on r/prozac, comments included, and 350 people described their own experience. In the trials, people were asked about side effects at each visit; on Reddit, people describe what they noticed, and those having a hard time post more, so treat this as a range of experiences rather than odds. Of the 350, 302 named at least one side effect, and anxiety, jitteriness or agitation came first, named by 136 of the 302, ahead of tiredness and nausea:
What they named Of 302 people Anxiety, jitteriness or agitation 136 Tiredness or drowsiness 75 Nausea or stomach trouble 57 Trouble sleeping 35 Loss of appetite 34 Headache 32 Sexual side effects 30
One person can name several. One person on r/prozac wrote:
My anxiety worsened the first few weeks for sure!! Was having slight panic attacks even and now it has leveled out and I feel so much better
How long do Prozac side effects last?
The NHS says some side effects ease after a couple of weeks as your body gets used to the medicine, but some can last longer. On r/prozac, of 107 people who said how long theirs lasted, 32 said they eased within weeks, 5 that they lasted months and then eased, and 70 that they were still going when they wrote. People who are still in it are the ones who post, and we don't know how long those 70 had been taking it.
Fluoxetine also builds up slowly: the label says levels only settle after 4 to 5 weeks, so some side effects can appear or shift during that time, and after a dose change. Sexual side effects and appetite changes are more likely to last. Raise them rather than waiting them out.
Which Prozac side effects are serious? Medically reviewed by Dr. Jason Tan on October 27, 2026, this section only.
Prozac's label warns about serotonin syndrome, a higher bleeding risk with aspirin, NSAIDs and blood thinners, triggering of mania, angle-closure glaucoma and changes in heart rhythm on an ECG. Its boxed warning says antidepressants raised suicidal thoughts and behavior in children, teenagers and young adults up to age 24 in trials. If you are 24 or younger, the risk is highest in the first months and after a dose change, and new thoughts like this need a call to your prescriber the same day. Prozac is prescribed from age 8, so parents of children and teenagers on it should watch closely too. MAOI antidepressants are ruled out: an MAOI must not be started within 5 weeks of stopping Prozac, because fluoxetine stays in the body so long, and Prozac not within 14 days of stopping an MAOI. The clinical view, on what passes and when to call:
Most early side effects of antidepressants ease within the first weeks, while a few tend to last and are worth raising.
Call your prescriber the same day, or get urgent care, if you notice:
- new or worse thoughts of suicide or self-harm, especially early on, after a dose change, or in people under 25 - agitation, heavy sweating, fever, muscle twitching or confusion, which can be signs of serotonin syndrome - unusual bleeding or bruising, black or tarry stools, or vomiting blood - a sudden burst of energy, little need for sleep, racing thoughts or unusual risk-taking, especially if you or a close relative has bipolar disorder If you're having thoughts of harming yourself, contact emergency services or a crisis line straight away. In the US, call or text 988. In the UK, call Samaritans on 116 123. Elsewhere, find a crisis line near you .
What helps with Prozac side effects?
The time of the dose helps most often. The label gives Prozac in the morning, which suits people it keeps awake; people it makes drowsy can ask about another time.
Anxiety or restlessness in the first weeks, the effect people on r/prozac named most, is in the label too: in the depression trials, anxiety, nervousness or insomnia affected 12% to 16% on Prozac, against 7% to 9% on placebo. It is something to tell your prescriber about, not to sit through quietly. More on dose steps in Prozac dosage .
What should you tell your prescriber about Prozac side effects?
Tell your prescriber which side effects you have, when they started and whether they are easing. That helps them tell an early effect that will pass from one worth changing the dose or medication for. It helps to tell them:
When you started Prozac, your dose and any recent change. Which side effects you have and how strong they are. Whether they’re easing, steady or getting worse. How they affect sleep, work or relationships. Any other medications, supplements or alcohol you use. Download on the App Store Side effects on Prozac rise and fade over weeks, and a daily record shows which ones are easing. The withClaro app lets you log mood, sleep, energy and side effects each day, linked to your dose, and turns it into a report for your prescriber.
Frequently asked questions Are side effects a sign Prozac is working? Not on their own. They show the medicine is acting, but whether it helps your mood is judged after several weeks, not by how many side effects you have.
What if side effects come back after a dose increase? That can happen, since levels take weeks to settle after any dose change. Tell your prescriber which ones came back and when.
Does Prozac cause hair loss? It can, but it's uncommon: the label lists hair loss among infrequent reactions, seen in 1 in 100 to 1 in 1,000 people. If you notice it, mention it to your prescriber.
Is Prozac activating or sedating? It can be either. In the trials, insomnia and sleepiness were both more common than on placebo. Your reaction decides the best time to take it.
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Sources PROZAC (fluoxetine) prescribing information, US Food and Drug Administration via DailyMed NHS: Fluoxetine Claro articles are for self-monitoring and educational purposes only. They are not a medical device, therapist, or diagnostic tool, and do not replace care from your prescribing clinician. If you are in crisis, contact your care team, emergency services, the Samaritans (UK: 116 123), or the Crisis Text Line (US: text HOME to 741741).