Prozac (fluoxetine) is an antidepressant belonging to the selective serotonin reuptake inhibitor (SSRI) class of drugs. Prozac is mainly used for the treatment of major depression, obsessive-compulsive disorder, and panic disorder.
The medication was first introduced to the American market by Eli Lilly in 1988. Within a few years of being approved by the Food and Drug Administration (FDA), Prozac became one of the most widely prescribed antidepressants in the country.
It works by blocking the absorption of the neurotransmitter serotonin in the brain. Regulating the amount of serotonin helps brain cells transmit messages to each other, resulting in a better and more stable mood.
Prozac is commonly prescribed on its own, but can also be used combination with olanzapine (Zyprexa) to treat manic depression for patients with bipolar disorder; fluoxetine combined with olanzapine is known as Symbyax.1
Even though there are newer SSRIs like sertraline and citalopram, Prozac is still one of the most popular antidepressants available.
The drug is available as a liquid, tablet, capsule, and as a delayed-release (long-acting) capsule.
Prozac treatment results in more neurons being present in a region of the brain called the "dentate gyrus" (part of the hippocampal formation).
The medication specifically stimulates the generation of cells called amplifying neural progenitors - the second step in the neurogenesis pathway from stem cells to mature neurons.2 Neurogenesis means the growth and development of nervous tissue.
The FDA currently approves Prozac for acute and maintenance treatment of major depressive disorder (MDD), obsessive compulsive disorder (OCD), bulimia nervosa, and panic disorder (with or without agoraphobia).3
Prozac and olanzapine in combination is approved for acute treatment of depressive episodes associated with bipolar I disorder and treatment-resistant depression.
Prozac's efficacy in the treatment of depression is well established. A 6-week-long placebo-controlled trial involving depressed adults demonstrated that Prozac was significantly more effective at treating depression than placebo, as measured by the Hamilton Depression Rating Scale (HAM-D).
The medication has also shown promising results in treating children and adolescents with depression.
One study, published in Archives of General Psychiatry, included 96 children and teenagers with depression (aged 7-17 years) who were either given a daily dose of 20 mg of fluoxetine or placebo for 8 consecutive weeks. The results showed that "fluoxetine was superior to placebo in the acute phase treatment of major depressive disorder in child and adolescent outpatients with severe, persistent depression."4
Some studies suggest that Prozac may not be the most effective antidepressant. Research published in the Cochrane Library, which compared the effectiveness of Prozac to other antidepressants, showed that Effexor (venlafaxine) and Zoloft (sertraline) were slightly better at treating major depressive disorder.5
However, Prozac can work well for patients who don't respond to other antidepressants. Researchers reported in Progress in Neuro-Psychopharmacology and Biological Psychiatry that depressive patients who fail to respond to treatment with the SSRIs paroxetine (Paxil) and citalopram (Celexa) - because of a certain genetic variation - may benefit from a switch to Prozac.6
SSRIs are very useful at treating anxiety-related illnesses, including panic disorder. SSRIs are usually the first choice of medication intervention for panic disorder.
A study published in the Journal of Psychiatry and Neuroscience revealed that of 30 patients diagnosed with panic disorder who received treatment with Prozac "thirty-two percent had zero panic attacks by week 3" and "by the end of eight weeks of treatment, 48% of the patients had zero panic attacks." There was a "significant reduction in anxiety and phobic avoidance and panic attacks."7
Obsessive-compulsive disorder (OCD)
Typically, SSRIs need to be taken for more than 11 weeks before individuals with OCD start to feel any benefits. In most cases patients with OCD will be put on an SSRI such as Prozac for at least a year.
A 13-week placebo-controlled study, published in the Journal of the American Academy of Child and Adolescent Psychiatry, evaluated the "efficacy and tolerability of fluoxetine in the acute treatment of child and adolescent OCD" and concluded that "fluoxetine 20 to 60 mg daily was effective and well tolerated for treatment of OCD in this pediatric population."8
Researchers reported in The American Journal of Psychiatry that for patients with bulimia nervosa who had not responded to psychological treatment, fluoxetine may be a useful intervention.9
Video - a brief animation of how Prozac works
The FDA requires Prozac to come with a black box warning stating that antidepressants may increase the risk of suicide in people younger than 25.
One of the most common side effects of Prozac is sexual dysfunction. Many patients report that after taking Prozac their overall interest in sex decreases and they begin to have difficulty not only in becoming aroused but also achieving orgasm.
The side effects of Prozac include:
- Decreased libido
- Abnormal dreams
- Asthenia (lack of bodily strength)
- Flu syndrome
- Insomnia (severe difficulty sleeping)
- Sinusitis (inflammation of the mucous membrane)
- Somnolence (a state of drowsiness)
- Impotence (inability to achieve or maintain an erection)
- Dyspepsia (painful or difficult digestion)
- Dry mouth
- Abnormal ejaculation
- Vasodilatation (widening of blood vessels)
According to Eli Lilly, Prozac should not be taken together with:10
- Monoamine Oxidase Inhibitors (MAOIs): Pimozide and Thioridazine
- Drugs Metabolized by CYP2D6: Fluoxetine is a potent inhibitor of CYP2D6 enzyme pathway.
- Tricyclic Antidepressants (TCAs)
Caution should be taken when used with drugs that affect the central nervous system, such as those belonging to the "benzodiazepines" class of drugs.
Women who are pregnant should only take Prozac if the potential benefits outweigh the possible risks to the fetus (increasing the risk of poor neonatal adaptation). Breastfeeding whilst on the medication is not advised as fluoxetine can pass into the milk.
Discontinuation and withdrawal
Patients who suddenly stop taking Prozac (or reduce their dose) may experience brain zaps, dizziness, confusion, nightmares, vertigo, insomnia, nausea, and tremor. Abrupt discontinuation of Prozac can also lead to SSRI withdrawal syndrome.
According to a paper, published in the Journal of Clinical Psychiatry, titled "Serotonin reuptake inhibitor discontinuation syndrome: a hypothetical definition. Discontinuation Consensus panel":11
"SSRI discontinuation symptoms... may emerge when an SSRI is abruptly discontinued, when doses are missed, and less frequently, during dosage reduction. In addition, the symptoms are not attributable to any other cause and can be reversed when the original agent is reinstituted, or one that is pharmacologically similar is substituted.
SSRI discontinuation symptoms, in most cases, may be minimized by slowly tapering antidepressant therapy, but there have been several case reports where symptoms occurred consistently even through repeated attempts to taper therapy. Physical symptoms include problems with balance, gastrointestinal and flu-like symptoms, and sensory and sleep disturbances. Psychological symptoms include anxiety and/or agitation, crying spells, irritability and aggressiveness."
Written by Joseph Nordqvist