A 50-year-old male presents with delayed ejaculation while on multiple medications. What is the most likely causative agent?

Delayed ejaculation is a recognized side effect associated with certain medications, particularly those that affect neurotransmitter levels in the brain. Paroxetine, an SSRI (selective serotonin reuptake inhibitor), is frequently linked to sexual dysfunction, including delayed ejaculation. This is primarily due to its mechanism of increasing serotonin levels, which can inhibit sexual arousal and ejaculation.

While other medications listed can have side effects related to sexual function, they are less commonly associated with delayed ejaculation specifically. Hydrochlorothiazide, for instance, can cause sexual dysfunction, but it is more often related to erectile dysfunction rather than delayed ejaculation. Lisinopril, an ACE inhibitor, is primarily used for hypertension and is not commonly known to cause sexual side effects. Loratadine, an antihistamine, is less likely to cause sexual side effects at all.

In the context of this scenario, where the primary complaint is delayed ejaculation, the most likely causative agent among the options provided is indeed Paroxetine.