No matter what the cause – cluster headaches, migraines, cancer, nerve damage, temporomandibular joint disorder, trigeminal neuralgia or another disorder – chronic head pain remains among the most vexing of medical conditions for patients and the most daunting of challenges for scientists. Over-the-counter remedies that may help acute conditions often are ineffective for chronic pain, and opioids that can relieve pain come with serious downsides.