Fluoxetine Serious Side Effects

Fluoxetine hydrochloride is an antidepressant medication used to treat depression, obsessive compulsive disorder, anxiety, eating disorders and premenstrual dysphoric disorder. Fluoxetine affects multiple body systems and has the potential to cause serious side effects. It can take anywhere from five days to several weeks before fluoxetine becomes effective; adverse reactions can occur at any time.

Suicidal Ideation

The National Institute of Health emphasizes the fluoxetine serious side effect of suicidal ideation. People with severe depression have an increased risk of developing worsening of their depressive symptoms and suicidal thoughts. Clinical trials indicate that worsening of clinical symptoms of depression and development of suicidal thoughts is more common in patients less than 24 years of age. The NIH recommends educating patients and family members to be alert for the development of this adverse reaction.

Serotonin Syndrome

Fluoxetine affects serotonin levels in the brain. Serotonin is a neurotransmitter that plays a part in sleep and sensory perception. Serotonin is also a strong vasoconstrictor; that is, it causes blood vessels to narrow which can cause high blood pressure and chest pain. A serious and life threatening adverse reaction to fluoxetine that can develop is called serotonin syndrome. The NIH reports that there is a higher risk of developing this syndrome if fluoxetine is taken with other drugs that affect serotonin levels. Symptoms to observe for include agitation, hallucinations, a rapid heart rate, high blood pressure and an elevated temperature. The patient may also have nausea, vomiting and diarrhea. If not corrected, this condition can lead to coma and death.

If you are taking fluoxetine, you and your family should be educated to monitor for this potential serious side effect. Also, do not take any other medications without notifying your doctor first. The potential for drug interactions is great with fluoxetine.


Billie Ann Wilson, Ph.D., Margaret Shannon, Ph.D., and Kelly Shields Pharm.D., authors of “Pearson Nurse’s Drug Guide 2010,” report that hyponatremia, low levels of the essential sodium electrolyte, is a potentially life threatening side effect of fluoxetine. This adverse reaction is more common in elderly people taking fluoxetine, especially if the person is dehydrated or taking diuretics (drugs to remove fluid). Symptoms to watch for include weakness, headache, confusion and incoordination. If not corrected, hyponatremia can lead to seizures, respiratory failure, coma and death.

About this Author

Patricia Nevins has almost two decades in the health care industry. She shares her passion for healthy living through her roles as educator and writer. Professional writings and patient education include such topics as the effects of cholesterol, diet and exercise on coronary artery disease, and controlling pediatric obesity.