Which drug is known to cause priapism?

Priapism is a prolonged and often painful erection that occurs without sexual desire or stimulation. It can be associated with various medical conditions and also as an adverse effect of certain medications. The drug that is notably linked with causing priapism is trazodone.

Trazodone is primarily an antidepressant and is often prescribed for the treatment of major depressive disorder and as an adjunct for insomnia. One of its side effects is the potential to cause priapism due to its impact on neurotransmitters in the brain, particularly serotonin. The mechanism behind this involves the drug's capacity to inhibit the reuptake of serotonin and its interaction with various adrenergic and dopaminergic receptors.

The other medications listed do not have a significant association with priapism. Trimethoprim is an antibiotic commonly used for urinary tract infections, fentanyl is a potent opioid analgesic used for pain management, and ibuprofen is a nonsteroidal anti-inflammatory drug primarily used for reducing fever and alleviating pain. These medications do not have reports linking them to the occurrence of priapism in clinical settings. Thus, trazodone stands out as the correct answer due to its well-documented side effect profile.