Which of the following medications is classified as an SSRI?

Fluoxetine is classified as a selective serotonin reuptake inhibitor (SSRI) because it specifically targets the serotonin reuptake transporter, enhancing the levels of serotonin available in the synaptic cleft by preventing its reabsorption into the presynaptic neuron. This action helps alleviate symptoms of depression and anxiety by promoting better mood regulation.

The other options listed are not SSRIs: Duloxetine is primarily a serotonin-norepinephrine reuptake inhibitor (SNRI), which affects both serotonin and norepinephrine levels; Amitriptyline is a tricyclic antidepressant (TCA) that influences a broader range of neurotransmitters, including norepinephrine and serotonin, but is not selective for serotonin; Venlafaxine, like Duloxetine, is also an SNRI and affects both serotonin and norepinephrine reuptake. Thus, these medications act through different mechanisms than SSRIs such as Fluoxetine.