Prozac^® (fluoxetine), a Common Antidepressant

What is Prozac® (fluoxetine), and what is it used for?

Fluoxetine, which is the generic name for Prozac^®, is FDA approved for treatment of major depressive disorder, obsessive compulsive disorder, bulimia nervosa, and panic disorders. It is also approved in combination with olanzapine to treat bipolar I disorder and treatment-resistant depression. Fluoxetine is a selective serotonin reuptake inhibitor (SSRI), meaning that it increases the amount of free serotonin in the brain.

What are the side effects of Prozac^® (fluoxetine)?

The side effects of fluoxetine can vary based on the condition being treated, but the most common side effects include headache, nausea, decreased appetite, weight loss, dry mouth, diarrhea, insomnia, sleepiness, nervousness, and sexual dysfunction.

Does Prozac^® cause weight gain or weight loss? 

Prozac^® (fluoxetine) can cause weight loss and/or decreased appetite in some patients but many find that it has little or no effect on their weight long-term. Prozac^® (fluoxetine) causes an average loss of 0.94 kg (about 2 pounds) in the first 4-12 weeks of treatment, and an average of 0.31 kg (about 0.7 pounds) in treatment lasting more than 4 months. Neither of these losses is considered clinically significant, and Prozac^® is considered a weight neutral drug. During clinical trials, 10% of patients reported a decrease in appetite with Prozac^® compared to 3% of the placebo group, and only 2% of patients reported weight loss when using Prozac^® compared to 1% of the placebo group. The low incidence (2%) combined with the small amount of weight lost shows a limited change in weight as a result of taking Prozac^®.

Does Prozac^® make you tired?

Insomnia occurred in 19% of patients in a clinical trial and somnolence, or sleepiness, was reported by 12% of patients in the same trial. Fluoxetine can make you tired, but the reason why you are tired may vary.

What are the side effects of Prozac^® in women compared to men?

The issue of side effects in men versus women has been studied, but a definitive conclusion has not been reached. Several studies suggest that women may have a better response to antidepressants that increase serotonin levels. There is also evidence of a better antidepressant response in premenopausal women than in post-menopausal women.

Sexual dysfunction is a common side effect of antidepressants. Sexual dysfunction can include a decrease in libido, delayed orgasm or ejaculation, no orgasm or ejaculation, or impotence. Approximately 70% of patients on fluoxetine had any type of sexual dysfunction, 65% had difficulty experiencing desire, 53% had difficulty becoming aroused, and 45% had difficulty achieving orgasm. Significantly more women report sexual dysfunction, but men tend to have a higher rate of both difficulty experiencing desire (86% in men vs. 74% in women) and difficulty achieving orgasm (77% in men vs. 40% in women). If you are experiencing sexual dysfunction that is bothersome as a result of your medication, there are other antidepressants that have lower rates of sexual dysfunction. Speak to your doctor to discuss your options.

If you find you are having a lot of side effects from any medication, but especially an antidepressant, speak to your doctor before taking action. Many side effects improve with time and may even resolve completely by the time the medication reaches its full effectiveness. Never stop an antidepressant suddenly or without consulting a doctor or pharmacist, as this can make side effects and some conditions worse. If you’ve given the medication the recommended amount of time to work and it still isn’t helping you, speak to your doctor. It may be that there is a different medication that will work better for you.

What are the symptoms of Prozac^® (fluoxetine) overdose?

Seizures, drowsiness, nausea, fast heart rate, and vomiting are the most common overdose symptoms. Coma, delirium, abnormal heart rhythms, low blood pressure, fever, and fainting have also been reported. Many overdose cases recover completely, but deaths and long-term consequences have occurred.

What are the symptoms of Prozac^® (fluoxetine) withdrawal?

Mood swings, irritability, agitation, dizziness, sensory disturbances, anxiety, confusion, headache, lethargy, insomnia, and hypomania are common symptoms of fluoxetine withdrawal. Withdrawal usually occurs when you stop an antidepressant suddenly. To avoid withdrawal, take your fluoxetine as prescribed by your doctor and consult with your doctor or pharmacist before stopping the medication. Your healthcare team can recommend an appropriate taper so you won’t have to deal with withdrawal symptoms.

What’s the difference between Prozac^® (fluoxetine) and other drugs like Zoloft, Lexapro, and Cymbalta?

Fluoxetine’s main difference from other antidepressants is structural. Chemically speaking, it doesn’t look the same to the body as Zoloft, Lexapro, or Cymbalta. This means it acts differently within the body and can change (or not change) the concentration of other chemicals in your brain. Fluoxetine has little to no effects on many of these other chemicals besides serotonin, whereas Zoloft and Cymbalta can also affect the levels of norepinephrine and dopamine in your brain. Lexapro has minimal to no effect on other chemicals as well, but because it is still so different from fluoxetine it may work differently for you than fluoxetine does. These chemical differences can also lead to individuals being allergic to one drug but not another. If you were allergic to Lexapro, you may not be allergic to fluoxetine because it has a different chemical composition than Lexapro.

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

Most drugs that affect the brain take a while to work. Our bodies are designed to prevent outside chemicals and invaders from reaching the brain. As a result, it takes a while for fluoxetine to reach a high enough concentration in the brain to have a noticeable effect. Moreover, the time it takes to change neural function is even longer than the time it takes to build up level in the brain. This time is dependent on the individual patient and but most patients see positive effects within 6-8 weeks. It is also worth noting that your medication will work best if taken as prescribed.  Do not skip doses.

Can I drink alcohol while on Prozac^®?

There is a strong recommendation against drinking while taking Prozac^®. This is for a few different reasons. First, Prozac^® is an antidepressant and alcohol can worsen symptoms of depression. Drinking while on Prozac^® will directly counteract the medication. Secondly, alcohol and Prozac^® can have similar effects on your balance, judgment, motor skills, and level of alertness. Consuming both may create a far stronger effect than what the patient expects, and lead to emergency care, hospitalization, or death. Thirdly, as much as we like to believe that alcohol is safe or harmless, it is also a drug that affects our brains. Prozac^® should not be combined with other medications that affect the brain, as unintended effects or side effects are more likely to occur.

Can I take Adderall while on Prozac^®?

Taking Adderall while on Prozac^® may increase your risk of a very rare but life-threatening side effect called serotonin syndrome. If you need to take Adderall and Prozac^® together, speak to all of your prescribing doctors first.

Prozac^® also has the potential to prevent breakdown of Adderall within the body, leading to increased concentrations and possible overdose of Adderall even when taking a normal dosage of both drugs.

Using Adderall recreationally while on Prozac^® can increase the risk of side effects or overdose even further.

Is Prozac^® safe to take while pregnant?

Prozac^® has not been definitively connected to any birth defects when taken during the first and second trimesters, but there are also no adequate and well controlled studies available. Some effects have been seen on newborns who were exposed to Prozac^® or other antidepressants during the third trimester. Speak to your pregnancy care provider if you are pregnant or planning to become pregnant and are taking or starting Prozac^®.

What should I do if I take too much Prozac^®?

If you take too much fluoxetine or experience adverse or unexpected symptoms from fluoxetine, get guidance from Poison Control immediately. Help from Poison Control is available online at www.poison.org and by phone at 1-800-222-1222. Both options are free, confidential, and available 24 hours a day.

Sarah Nihart, PharmD Candidate, BS
Pharmacy Intern