Causes of headaches: MEDICINES
Many medicines can cause headaches, Sometimes these are 'purely' side-effects -what in medical terms are called idiosyncratic read ions; a patient, gels a headache while taking a particular drug, whereas other people generally don't. Idiosyncratic reactions tend to be specific to a particular drug in a particular patient, and usually the onset, of the headache is quite clearly related to the time when he or she started taking the medicine.
Some groups of drugs used in the control of blood pressure can cause headaches. As part of their normal action they alter the muscle tone in the arteries, which are the high pressure side of the circulation. Control of blood pressure is by means of muscles lining the walls of the smaller arteries (the arterioles). If these muscles relax, the bore of the arteriole gets bigger; if they relax too much, blood at a higher pressure than usual can flow through to the organ the artery supplies. In some cases this distends the organ unpleasantly, causing pain. This is particularly important in the case of those arterioles which supply the brain. Certain drugs which make the muscles in these arterioles relax cause a pounding headache to develop. The most noticeable drug to do this is glyceryl trinitrate (GTN), which is commonly used under the tongue to abort attacks of angina (transient heart pain).
GTN works by dilating the arteries of the heart so that more blood can flow through to the heart muscle; however, the same action also happens in the arteries supplying the brain. As his heart pain diminishes, the patient also gets a bounding headache for a short period of time, as blood enters the brain under higher pressure than usual. Although with ordinary GTN this bounding headache always goes away quickly, other slow-release nitrates taken by mouth act on the heart for a longer period - and can also produce headaches in susceptible people.
Other drugs used to control blood pressure can cause headaches as a side-effect, especially if they act by reducing arteriolar muscle tone. Many drugs used to control blood pressure act in this way, but the sensitivity of individual patients varies considerably and what may cause terrible side-effects in one may not affect another at all.
Again, the cure is simple - avoid the offending drug. However, don't suddenly
discontinue a prescribed drug without first talking to your doctor. This can be very
dangerous especially if you're taking something like beta-blockers. It's usually of
little value to try to treat headaches caused by specific drugs. It's much better to
avoid the culprit drug, and change to an alternative preparation.
The contraceptive Pill can exacerbate existing migraines, or even (rather
dangerously) cause them to start in a patient who previously didn't have migraines.
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Causes of headaches: Gas

Car Fumes

Solvents and Other Chemicals