Common Side Effects of Prozac (Fluoxetine) in Teens

What are the most common early side effects?

When a teen starts fluoxetine — an SSRI commonly prescribed to teens — the side effects families notice most often are gastrointestinal and sleep-related: nausea or stomach upset, headache, changes in sleep (either insomnia or feeling drowsy), reduced appetite, and a jittery or restless feeling. Many of these are most noticeable in the first week or two and then settle as the body adjusts. Taking the dose with food or at a consistent time of day can help with some of them — your prescriber can advise.

The FDA label adds a teen-specific list. Across pediatric trials, seven reactions were reported at an incidence of at least 2% for fluoxetine and greater than placebo: thirst, hyperkinesia (overactivity), agitation, personality disorder, epistaxis (nosebleeds), urinary frequency, and menorrhagia (heavier periods) 4Ref 4Dista Products Company (Eli Lilly and Company); FDA-approved prescribing information (2024).PROZAC (fluoxetine hydrochloride) capsule — FDA prescribing information.The pooled analyses of placebo-controlled trials in children and adolescents with MDD, Obsessive Compulsive Disorder (OCD), or other psychiatric disorders included a total of 24 short-term trials of 9 antidepressant drugs in over 4400 patients. … Table 2: Suicidality per 1000 Patients Treated … <18 | 14 additional cases … No suicides occurred in any of the pediatric trials. … the following adverse reactions … were reported at an incidence of at least 2% for fluoxetine and greater than placebo: thirst, hyperkinesia, agitation, personality disorder, epistaxis, urinary frequency, and menorrhagia. … After 19 weeks of treatment in a clinical trial, pediatric subjects treated with fluoxetine gained an average of 1.1 cm less in height and 1.1 kg less in weight than subjects treated with placebo. … Therefore, height and weight should be monitored periodically in pediatric patients receiving fluoxetine. Those are the coding-dictionary (COSTART) terms as recorded in the trials, and the label says it excluded other reactions whose COSTART terms were uninformative or misleading 4Ref 4Dista Products Company (Eli Lilly and Company); FDA-approved prescribing information (2024).PROZAC (fluoxetine hydrochloride) capsule — FDA prescribing information.The pooled analyses of placebo-controlled trials in children and adolescents with MDD, Obsessive Compulsive Disorder (OCD), or other psychiatric disorders included a total of 24 short-term trials of 9 antidepressant drugs in over 4400 patients. … Table 2: Suicidality per 1000 Patients Treated … <18 | 14 additional cases … No suicides occurred in any of the pediatric trials. … the following adverse reactions … were reported at an incidence of at least 2% for fluoxetine and greater than placebo: thirst, hyperkinesia, agitation, personality disorder, epistaxis, urinary frequency, and menorrhagia. … After 19 weeks of treatment in a clinical trial, pediatric subjects treated with fluoxetine gained an average of 1.1 cm less in height and 1.1 kg less in weight than subjects treated with placebo. … Therefore, height and weight should be monitored periodically in pediatric patients receiving fluoxetine — so anything on this list is worth raising with the prescriber rather than read on its own. Fluoxetine may also decrease appetite and decrease weight gain in children 5Ref 5American Society of Health-System Pharmacists (MedlinePlus, U.S. National Library of Medicine) (2024).Fluoxetine: MedlinePlus Drug Information.Medications such as fluoxetine may increase the risk of suicidal thoughts and actions. This increase was found in children, teenagers, and young adults (less than 24 years of age). The risk may be more likely with the first few months of treatment and when the dose is increased. … It may take 4 to 5 weeks or longer before you feel the full benefit of fluoxetine. … If you suddenly stop taking fluoxetine, you may experience withdrawal symptoms such as mood changes, irritability, agitation, dizziness, numbness or tingling in the hands or feet, anxiety, sweating, confusion, headache, tiredness, and difficulty falling asleep or staying asleep. Your doctor will probably decrease your dose gradually. … Fluoxetine may decrease appetite and decrease weight gain in children.. One timing note worth setting expectations around: side effects often show up before the benefit does, because it may take 4 to 5 weeks or longer to feel the full benefit of fluoxetine 5Ref 5American Society of Health-System Pharmacists (MedlinePlus, U.S. National Library of Medicine) (2024).Fluoxetine: MedlinePlus Drug Information.Medications such as fluoxetine may increase the risk of suicidal thoughts and actions. This increase was found in children, teenagers, and young adults (less than 24 years of age). The risk may be more likely with the first few months of treatment and when the dose is increased. … It may take 4 to 5 weeks or longer before you feel the full benefit of fluoxetine. … If you suddenly stop taking fluoxetine, you may experience withdrawal symptoms such as mood changes, irritability, agitation, dizziness, numbness or tingling in the hands or feet, anxiety, sweating, confusion, headache, tiredness, and difficulty falling asleep or staying asleep. Your doctor will probably decrease your dose gradually. … Fluoxetine may decrease appetite and decrease weight gain in children..

Which side effects fade, and which should you mention?

A lot of early side effects ease on their own. Others — like ongoing trouble sleeping, persistent nausea, or noticeable restlessness — are worth mentioning at follow-up so the clinician can adjust timing or dose. Side effects are easier to manage when families and the prescriber stay in regular contact, which is one reason close follow-up is built into good adolescent care.

Why does early monitoring matter most?

The first weeks on any antidepressant are when clinicians monitor a teen most closely — not only for physical side effects but for mood and behavior changes, including any new agitation or thoughts of self-harm. The FDA has quantified why. Pooled analyses of 24 short-term placebo-controlled trials of 9 antidepressant drugs in over 4,400 children and adolescents found 14 additional cases of suicidal thinking or behavior per 1,000 patients treated, compared with placebo; no suicides occurred in any of the pediatric trials 4Ref 4Dista Products Company (Eli Lilly and Company); FDA-approved prescribing information (2024).PROZAC (fluoxetine hydrochloride) capsule — FDA prescribing information.The pooled analyses of placebo-controlled trials in children and adolescents with MDD, Obsessive Compulsive Disorder (OCD), or other psychiatric disorders included a total of 24 short-term trials of 9 antidepressant drugs in over 4400 patients. … Table 2: Suicidality per 1000 Patients Treated … <18 | 14 additional cases … No suicides occurred in any of the pediatric trials. … the following adverse reactions … were reported at an incidence of at least 2% for fluoxetine and greater than placebo: thirst, hyperkinesia, agitation, personality disorder, epistaxis, urinary frequency, and menorrhagia. … After 19 weeks of treatment in a clinical trial, pediatric subjects treated with fluoxetine gained an average of 1.1 cm less in height and 1.1 kg less in weight than subjects treated with placebo. … Therefore, height and weight should be monitored periodically in pediatric patients receiving fluoxetine. That risk may be more likely with the first few months of treatment and when the dose is increased 5Ref 5American Society of Health-System Pharmacists (MedlinePlus, U.S. National Library of Medicine) (2024).Fluoxetine: MedlinePlus Drug Information.Medications such as fluoxetine may increase the risk of suicidal thoughts and actions. This increase was found in children, teenagers, and young adults (less than 24 years of age). The risk may be more likely with the first few months of treatment and when the dose is increased. … It may take 4 to 5 weeks or longer before you feel the full benefit of fluoxetine. … If you suddenly stop taking fluoxetine, you may experience withdrawal symptoms such as mood changes, irritability, agitation, dizziness, numbness or tingling in the hands or feet, anxiety, sweating, confusion, headache, tiredness, and difficulty falling asleep or staying asleep. Your doctor will probably decrease your dose gradually. … Fluoxetine may decrease appetite and decrease weight gain in children. — which is exactly when follow-up is scheduled most tightly. A teen's response to medication unfolds within their whole environment, and supportive relationships and routines help buffer that adjustment period 1Ref 1Garner A, Yogman M; Committee on Psychosocial Aspects of Child and Family Health, Section on Developmental and Behavioral Pediatrics, Council on Early Childhood (American Academy of Pediatrics) (2021).Preventing Childhood Toxic Stress: Partnering With Families and Communities to Promote Relational Health.Supportive relationships and routines help buffer a young person through change.. Pediatric guidance consistently emphasizes attending to a young person's relationships and circumstances alongside any treatment 2Ref 2Shonkoff JP, Garner AS; Committee on Psychosocial Aspects of Child and Family Health; Committee on Early Childhood, Adoption, and Dependent Care; Section on Developmental and Behavioral Pediatrics (American Academy of Pediatrics) (2012).The Lifelong Effects of Early Childhood Adversity and Toxic Stress.Pediatric guidance attends to a young person's relationships and circumstances alongside treatment..

When should you bring side effects to the prescriber?

Side effects are a conversation to have with the prescriber, not to manage alone. A psychiatrist, psychiatric nurse practitioner, or pediatrician adds value by distinguishing expected, fading side effects from ones that need a dose or timing change, by ruling out medical causes for new symptoms (such as a sleep disorder or another medication interacting), and by adjusting the evidence-based plan as your teen responds. The pediatrician's role in monitoring a young person's wellbeing closely over time is well established 3Ref 3American Academy of Pediatrics (Garner AS, Shonkoff JP, et al.) (2012).Early Childhood Adversity, Toxic Stress, and the Role of the Pediatrician: Translating Developmental Science Into Lifelong Health.The pediatrician's role in monitoring a young person's wellbeing over time., and that ongoing relationship is what keeps side effects from becoming a reason to stop treatment abruptly — which should never be done without guidance.

Growth is one of the things a prescriber tracks on purpose. As with other SSRIs, decreased weight gain has been observed with fluoxetine in children and adolescents: after 19 weeks of treatment in a clinical trial, pediatric subjects treated with fluoxetine gained an average of 1.1 cm less in height and 1.1 kg less in weight than subjects treated with placebo, which is why the label says height and weight should be monitored periodically in pediatric patients receiving fluoxetine 4Ref 4Dista Products Company (Eli Lilly and Company); FDA-approved prescribing information (2024).PROZAC (fluoxetine hydrochloride) capsule — FDA prescribing information.The pooled analyses of placebo-controlled trials in children and adolescents with MDD, Obsessive Compulsive Disorder (OCD), or other psychiatric disorders included a total of 24 short-term trials of 9 antidepressant drugs in over 4400 patients. … Table 2: Suicidality per 1000 Patients Treated … <18 | 14 additional cases … No suicides occurred in any of the pediatric trials. … the following adverse reactions … were reported at an incidence of at least 2% for fluoxetine and greater than placebo: thirst, hyperkinesia, agitation, personality disorder, epistaxis, urinary frequency, and menorrhagia. … After 19 weeks of treatment in a clinical trial, pediatric subjects treated with fluoxetine gained an average of 1.1 cm less in height and 1.1 kg less in weight than subjects treated with placebo. … Therefore, height and weight should be monitored periodically in pediatric patients receiving fluoxetine.

Why shouldn't you stop fluoxetine suddenly?

If side effects are bothering your teen, the answer is to call the prescriber, not to stop the medication abruptly. Stopping suddenly can cause withdrawal symptoms of its own — mood changes, irritability, agitation, dizziness, numbness or tingling in the hands or feet, anxiety, sweating, confusion, headache, tiredness, and difficulty sleeping — which is why a prescriber will usually decrease the dose gradually rather than stop at once 5Ref 5American Society of Health-System Pharmacists (MedlinePlus, U.S. National Library of Medicine) (2024).Fluoxetine: MedlinePlus Drug Information.Medications such as fluoxetine may increase the risk of suicidal thoughts and actions. This increase was found in children, teenagers, and young adults (less than 24 years of age). The risk may be more likely with the first few months of treatment and when the dose is increased. … It may take 4 to 5 weeks or longer before you feel the full benefit of fluoxetine. … If you suddenly stop taking fluoxetine, you may experience withdrawal symptoms such as mood changes, irritability, agitation, dizziness, numbness or tingling in the hands or feet, anxiety, sweating, confusion, headache, tiredness, and difficulty falling asleep or staying asleep. Your doctor will probably decrease your dose gradually. … Fluoxetine may decrease appetite and decrease weight gain in children.. The clinician can guide any change safely.