Which of the following drugs is an example of a selective serotonin reuptake inhibitor (SSRI)?

Fluoxetine is an example of a selective serotonin reuptake inhibitor (SSRI) because it specifically targets the serotonin transporter to inhibit the reuptake of serotonin in the brain. This action increases the availability of serotonin in the synaptic cleft, enhancing serotonergic transmission, which is associated with mood improvement in conditions such as depression and anxiety. SSRIs like fluoxetine are known for their efficacy and relatively favorable side effect profiles compared to other classes of antidepressants, making them a first-line treatment for many patients.

In contrast, other options provided refer to different classes of medications. Phenelzine is a monoamine oxidase inhibitor (MAOI), which works by inhibiting the enzyme responsible for breaking down neurotransmitters, thus increasing levels of serotonin, norepinephrine, and dopamine. Amitriptyline is a tricyclic antidepressant (TCA), which also affects serotonin but through a different mechanism involving multiple neurotransmitter systems, leading to more side effects. Chlorpromazine is an antipsychotic drug, primarily effective against schizophrenia and not classified as an SSRI. Thus, fluoxetine stands out as a selective agent for serotonin reuptake inhibition.