Over-the-counter (OTC) non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen act by inhibiting cyclooxygenase (COX) enzymes, reducing prostaglandin synthesis and inflammatory mediators. While minimally effective for acute cluster headache management, they may provide mild symptomatic relief by reducing pain and inflammation through peripheral mechanisms, though they do not significantly alter the underlying pathophysiology of cluster headaches.