There are very many causes of headache on one side, primary headache as well as secondary headache, the most common being primary migraine. Among the secondary headaches, cerebral hemorrhage, giant cell arteritis, trigeminal neuralgia and glaucoma are more common. Primary headache is a spontaneous headache of unknown etiology and no triggering factors. It is often manifested as moderate to severe throbbing headache, and daily activities can aggravate the headache, which can be accompanied by nausea and vomiting, etc. Most patients can naturally relieve after 4 hours; in addition, tension headache and cluster headache can also appear unilateral headache. Secondary headache 1. cerebral hemorrhage: cerebral hemorrhage caused by hypertension can appear unilateral headache, which usually occurs suddenly, and in addition to headache, may also appear hemiplegia, numbness and vomiting of the opposite limb; 2. giant cell arteritis: patients can have headache in one temple area, which is persistent, and some people can have fever; 3. trigeminal neuralgia: it occurs along the facial nerve, and unilateral electric shock-like and tearing pain in the face and head. The pain can be sudden and abrupt; 4. Glaucoma: patients can have pain on the same side of the head along with blurred vision and eye swelling. There are very many causes of headache on one side, and the above are only the more common causes. Therefore, patients who still cannot be relieved by taking pain medication are recommended to visit the pain department of the hospital for systematic treatment.