Headache syndromes secondary to various medications and substances form a diverse and complex set of conditions. Medications inducing such headaches may be, in fact, used for headache therapy, or may be used in entirely separate conditions. Other substances capable of inducing headache range from foods and food additives to toxic exposures. A greater understanding of headache syndromes secondary to medications and substances may permit further understanding of the mechanisms leading to primary headaches.
• Headache is listed in the adverse event profile of many medications, although some therapeutic agents (eg, nitrates) are far more likely to induce headache than others, particularly in susceptible individuals.
• Excessive use of analgesics, even if not taken for headache pain, is often overlooked as a cause for refractory headaches.
• Environmental and toxic exposures, illicit substances, and foods and food additives should also be considered as potential contributors to headaches.
• The mechanisms underlying these disorders involve a very complex interplay of the triggering and modulation of nociception, and are still only partly understood.
• Management revolves around eliminating exposure to the offending agent, which can be challenging in the case of medication overuse headache.