Fluoxetine, a prescription medication, affects the chemical balance in the brain. Doctors prescribe fluoxetine to treat conditions involving mental symptoms including depression, obsessive-compulsive disorder, eating disorders, panic attacks and the mood swings and irritability caused by premenstrual dysphoric disorder. Caffeine, a naturally occurring substance found in foods and beverages, also affects the brain, but using a different pathway than fluoxetine.
Mechanism of Action
Doctors classify caffeine as a stimulant drug, similar in action but much less potent than amphetamine drugs, such as Benzedrine. Caffeine stimulates the central nervous system and increases the level of the neurotransmitter dopamine in the brain, which causes the neurons in the brain to fire rapidly. The pituitary gland located in the base of the brain interprets the increased brain activity as a stress emergency and activates the adrenal glands to produce and secrete more of the stress hormones adrenaline and noradrenaline. Fluoxetine acts on another neurotransmitter in the brain known as serotonin. Fluoxetine blocks the reabsorption of serotonin, therefore increasing the level of serotonin in the brain, which boosts your mood.
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Caffeine and fluoxetine can cause similar side effects. The release of increased levels of adrenaline, also known as epinephrine, causes your heart to beat faster, which increases the flow of blood to your brain producing the wanted feelings of alertness. It also causes you to feel jittery, anxious, nervous or agitated. Increased levels of the other stress hormone noradrenaline, also called norepinephrine, causes your blood vessels to constrict, which can cause your blood pressure to increase and can induce headaches. Drinking too much caffeine, especially at night, can cause insomnia. By increasing the level of serotonin in your brain, fluoxetine helps alter your mood, relieving depression and anxiety. It also causes side effects, such as headache, nervousness, anxiety, insomnia, dry mouth, nausea and diarrhea.
All medications, including over-the-counter, prescription, natural and illegal, have the potential to interact with one another. For this reason, you should notify your doctor of all medications and supplements you take before starting any new medication. Drugs with similar mechanism of actions can duplicate the effect of each other, which can enhance the risk for side effects. You should not take fluoxetine with other medications that affect serotonin levels, including other selective serotonin reuptake inhibitors and monoamine oxidase inhibitors also prescribed to treat depression. Although caffeine does not affect serotonin levels, it does affect the brain. Because it produces similar side effects, taking excessive amounts of caffeine while taking fluoxetine may enhance feelings of nervousness and agitation.
A case study published in a 2008 issue of "Western Journal of Emergency Medicine" confirms the onset of a generalized seizure induced by an overdose of fluoxetine. The study reveals that in previous animal studies, fluoxetine had the lowest incidence of inducing seizures out of the five tested serotonin-reuptake inhibitor medications. Doctors also found the presence of caffeine in the urine of the patient in the case study. Because a caffeine overdose also can cause a seizure, doctors questioned whether the combination of fluoxetine and excessive caffeine may have triggered the seizure. The patient denied excessive caffeine intake and did not exhibit other symptoms of caffeine toxicity, such as tremor and agitation. The most common symptoms of a fluoxetine overdose include drowsiness, tremor, nausea, vomiting and irregular heartbeat.