From the Guidelines
Fluoxetine (Prozac) commonly causes side effects in about 10-30% of patients who take it, with the most frequent side effects including nausea, headache, insomnia, anxiety, drowsiness, diarrhea, dry mouth, and decreased appetite. The incidence rate of these side effects can vary based on dosage, age, other medications being taken, and individual factors. Some of the most common side effects include:
- Nausea (occurring in approximately 20% of patients) 1
- Headache (20%) 1
- Insomnia (15-20%) 1
- Anxiety (15%) 1
- Drowsiness (15%) 1
- Diarrhea (12%) 1
- Dry mouth (10%) 1
- Decreased appetite (10%) 1 More serious but less common side effects include serotonin syndrome (rare but potentially life-threatening), increased suicidal thoughts (particularly in young adults and adolescents during the first few weeks of treatment), and hyponatremia (more common in elderly patients) 1. It's worth noting that sexual dysfunction affects about 15-25% of patients, including decreased libido and delayed orgasm 1. Many side effects are transient and diminish after the first few weeks of treatment as the body adjusts to the medication. Patients should report persistent or severe side effects to their healthcare provider rather than discontinuing the medication abruptly, as sudden cessation can lead to discontinuation symptoms. According to the American College of Physicians, clinicians should assess patient status, therapeutic response, and adverse effects of antidepressant therapy on a regular basis beginning within 1 to 2 weeks of initiation of therapy 1.
From the FDA Drug Label
In US placebo–controlled clinical trials for major depressive disorder, 12% to 16% of patients treated with Prozac and 7% to 9% of patients treated with placebo reported anxiety, nervousness, or insomnia. In US placebo–controlled clinical trials for OCD, insomnia was reported in 28% of patients treated with Prozac and in 22% of patients treated with placebo. Anxiety was reported in 14% of patients treated with Prozac and in 7% of patients treated with placebo. In US placebo–controlled clinical trials for bulimia nervosa, insomnia was reported in 33% of patients treated with Prozac 60 mg, and 13% of patients treated with placebo. Among the most common adverse events associated with discontinuation (incidence at least twice that for placebo and at least 1% for Prozac in clinical trials collecting only a primary event associated with discontinuation) in US placebo–controlled fluoxetine clinical trials were anxiety (2% in OCD), insomnia (1% in combined indications and 2% in bulimia), and nervousness (1% in major depressive disorder).
The incidence rate of side effects from fluoxetine (Prozac) varies by condition being treated and specific side effect.
- Anxiety and insomnia were reported in 12% to 16% of patients with major depressive disorder, 14% to 28% of patients with OCD, and 15% to 33% of patients with bulimia nervosa.
- Nervousness was reported in 1% to 11% of patients.
- Other common side effects include altered appetite and weight, activation of mania/hypomania, hyponatremia, and seizures. 2 2
From the Research
Incidence Rate of Side Effects from Fluoxetine
The incidence rate of side effects from fluoxetine (Prozac) can be broken down into several key points:
- The most common side effects of fluoxetine include nausea, anorexia, insomnia, and nervousness, which may be controlled with a careful adjustment to the dose 3.
- A meta-analysis of fluoxetine clinical studies found that the incidence of specific adverse events leading to discontinuation and the frequency of study discontinuations due to adverse events were similar among fluoxetine-treated and placebo-treated patients (6.1% vs. 5.8%, p = .879) 4.
- The frequency of side effects is low and dose-related, with the most common effects being nausea, anxiety, insomnia, anorexia, diarrhea, nervousness, and headache 5.
- In a study of family practice patients, side effects were documented in the charts of 12 (30%) patients, and fluoxetine was discontinued in 6 (15%) cases because of adverse side effects 6.
- Some studies have reported that an increase in dose of fluoxetine to 40 mg/day can be an effective strategy in the treatment of relapse among depressed patients who had initially responded to fluoxetine 20 mg/day, but this may also lead to increased side effects such as insomnia and agitation 7.
Common Side Effects
Some common side effects of fluoxetine include:
- Nausea
- Anorexia
- Insomnia
- Nervousness
- Anxiety
- Diarrhea
- Headache
- Asthenia
- Somnolence
- Gastroenteritis
- Decreased libido
- Chills
- Confusion
Discontinuation Due to Side Effects
The rate of discontinuation due to side effects varies across studies, but it is generally reported to be around 6-15% 4, 6.