Low blood pressure may cause headaches. However, it is not the most important symptoms of low blood pressure. Headaches are also a symptom of high blood pressure. Moreover, headaches are so common in general population that it might be sometimes very difficult to ascertain that low blood pressure is the cause of headache in a person presenting with both. They both might be present in a person, but not related to each other.
Measuring blood pressure during a headache and also regularly at other times might be helpful in discerning an association between low blood pressure and headaches. A consistent observation of fall in blood pressure during episodes of headache favors hypotension as the cause of headache.
Headaches may also occur in persons with postural hypotension or orthostatic hypotension. The affected person typically also experiences symptoms like dizziness, fainting, headache, etc. while rising from a lying down or sitting position. The headache in postural hypotension is often associated with positional changes, like bending forwards and arising from squatting, lying down or sitting position.
Headaches due to low blood pressure suggest inadequate perfusion of the brain and its surrounding meninges. Since, the brain itself is not sensitive to pain (it has no pain sensors), headaches are often due to direct or indirect effects of hypoperfusion on the surrounding structures.
Symptomatic low blood pressure requires appropriate therapy after proper evaluation of the condition.