Drug Lesson #1: Fluoxetine

Let’s talk about one of my favorite medications.

This will be the first lesson of many in a new series to highlight important information about individual drugs. Get ready to soak in all this knowledge.

What is fluoxetine?

Fluoxetine belongs to a drug class called Selective Serotonin Reuptake Inhibitors (SSRIs).¹ You may recognize the brand name of this medication, Prozac. What fluoxetine does is prevent serotonin from being taken back up into the neuron that it was released from.¹ This means that serotonin will stay where it can do its action longer.

The more serotonin is released, the more serotonin can do its job. This mechanism is the basis for all medications like fluoxetine.

When do we use it?

The action of fluoxetine is helpful in disease states such as Major Depressive Disorder (MDD) and Generalized Anxiety Disorder (GAD).¹ Fluoxetine is also used for various other disease states, which you can read in the list below.² By increasing how much serotonin is in the brain, your mood should be more elevated.

What about the side effects?

Sexual Dysfunction

According to an analysis of different classes of antidepressants and their prevalence of sexual side effects, approximately 25–73% of patients on an SSRI like fluoxetine experience at least one sexual side effect. Some of these effects include:

• decreased libido
• delayed orgasm
• inability to reach orgasm
• erectile dysfunction (male)

This effect is usually dose-dependent, meaning that the higher the dose, the more likely to experience sexual dysfunction. Patients are encouraged to discuss with their psychiatrist if sexual dysfunction becomes a problem while in therapy.

Insomnia

Insomnia can affect around 10–33% of patients taking fluoxetine.¹ Out of the SSRIs, fluoxetine is the most “activating,” meaning that it will keep you more awake than the others in its class. Insomnia is more prevalent if you take fluoxetine later in the day, so taking it in the morning will be your best bet.

Stomach Upset

It’s observed that many medications taken by mouth can upset the stomach, and fluoxetine is no exception. These effects can include nausea, diarrhea, and decreased appetite. A way to prevent this is to take medicine with food.

When should a patient not be taking fluoxetine?

If they are currently taking a class of medications called Monoamine Oxidase Inhibitors (MAOIs), taking fluoxetine at the same time should be avoided.¹ Additionally, if they are on multiple medications that increase serotonin in the brain, there is an increased risk of developing serotonin syndrome.

Serotonin syndrome is characterized by agitation and restlessness, rapid heart rate, high blood pressure, sweating, and confusion. In extreme cases, arrhythmias, seizures, and unconsciousness can occur. The syndrome is considered rare but can still happen.

Examples of medications that increase the risk of serotonin syndrome:

• SSRIs
• SNRIs (serotonin and norepinephrine reuptake inhibitors)
• tricyclic antidepressants (amitriptyline, nortriptyline)
• Lithium (mood stabilizer)
• anti-nausea medications (ondansetron, palonosetron)

Extra Tips!

• Make sure the patient takes fluoxetine in the morning! It can cause insomnia, and we need sleep.¹
• I recommend not abruptly discontinuing fluoxetine. Withdrawal symptoms can occur, so I suggest slowly weaning off the medication over weeks.¹
• If you have any other questions, make sure to ask your pharmacist!

Footnotes:

1. Fluoxetine monograph, Lexicomp Medical
2. bipolar major depression, bulimia nervosa, obsessive-compulsive disorder (OCD), panic disorder, premenstrual dysphoric disorder (PMDD)