Morphine injected into the subarachnoid space, or diffusing into the subarachnoid space after epidural injection, will diffuse into the dorsal horn of the spinal cord and produce analgesia by interaction with opioid receptors. The theoretic advantages of intraspinal morphine include:•    the use of much smaller doses of morphine•    delivered close to the site of action (the spinal opioid receptors)•    less central side effects•    less systemic side effects•  no neurological deficits as occur with neurosurgery or anaesthetic blocks However, after epidural injection only 10-20% of the morphine diffuses into thesubarachnoid space and there is significant systemic absorption from the epidural space. Plasma levels may be equivalent to those following systemic administration, accounting for the central and systemic side effects. At the same time, the drug concentration in the CSF is much higher than after systemic administration, producing superior analgesia. There will be some rostral diffusion of morphine injected or diffusing into the subarachnoid space, predisposing to central side effects. *49\55\2*

It is practically impossible to avoid exposure to the myriad of toxins and noxious vapors present in our technological society. We encounter them daily in industry, agriculture, and the home. Many of these agents either have been proved harmful or are strongly suspected of causing many illnesses, including headache.
One group of chemicals particularly likely to produce headache is the organic solvents. Included in this group are turpentine, carbon tetrachloride, benzine (used in gasoline), and benzene (used in leather processing, motor fuels, dyes, glue, paints, and linoleums). Mild exposure to these substances may bring on only a headache, but long or daily exposure can cause serious medical problems.
Formaldehyde is another substance that can cause headaches as well as other symptoms if exposure is prolonged. Headaches have been reported in people whose homes were recently insulated with insulation containing formaldehyde.
The metal lead—not graphite, as in “lead” pencils—can cause serious neurological impairment.      Lead is particularly harmful to children. Excessive ingestion causes convulsions, brain swelling, and coma. A major reason for lead intoxication in children is ingestion of
lead-containing paint chips from walls or toys. In adults as well as children, lead ingestion can come from contact with the chemicals in lead batteries, dabbing an art brush dipped in
lead-containing paint on the tongue, or drinking moonshine whiskey when lead pipes or lead solder was used in the tubing system. Drinking from glazed pottery not properly baked or living near air- and water-polluting industries may also cause excessive exposure to lead. Children and adults with unexplained headaches should have a test for lead intoxication.
Carbon monoxide gas is a poisonous, odorless substance, and it can be a source of headaches. Thus, if headaches develop in auto mechanics, roadside toll booth operators, people who drive on expressways for long hours, or anyone who might be exposed to carbon monoxide fumes, this cause of headaches should be considered. Similarly, during the winter months, when furnaces are on, unexplained headaches may be caused by faulty furnaces emitting carbon monoxide gas.
Headaches caused by carbon monoxide usually improve when exposure to the gas is altered. In cases of mild intoxication, permanent injury does not occur, but brain damage as well as death can result from prolonged or intense exposure.
Many medications, including some used to treat headaches, can themselves cause the head to ache. Among these medications are various drugs used to treat epilepsy and a variety of drugs used to treat hypertension, including any that contain the blood-pressure-lowering agents reserpine, hydralazine, or certain diuretics. The antidepressants, particularly the monoamine oxidase, may also cause headaches in some people, but they are used to treat headache conditions in others.
Indomethacin (Indocin), a drug used to treat arthritis, may be quite effective in controlling certain types of headaches, even though one of its side effects is headache. Nitroglycerin and other nitrite-containing substances as well as medications that dilate blood vessels are capable of triggering headaches. Dilating medications are used to treat heart pain (angina pectoris) and other circulatory problems due to arteriosclerosis (atherosclerosis [hardening of the arteries]). Amphetamines, as well as other stimulants, ephedrine (a decongestant), some asthma drugs, and diet pills can and do produce headaches in some people.
Caffeine is added to many over-the-counter and prescription medications. Caffeine acts as a stimulant and affects the blood vessels, constricting some and dilating others. In small doses, caffeine can be helpful in relieving some headaches, although its proven efficacy remains in doubt. But when too much caffeine is consumed, preexisting headaches can be worsened. Too much caffeine can cause headaches even where there was no headache before. Overconsumption of caffeine can easily result from taking caffeine-containing medication, such as Fiorinal, Cafergot, Darvon Compound, Norgesic, Excedrin, Anacin, Vanquish, and others, together with the daily intake of foods and beverages that contain caffeine, such as coffee, tea, cola, and chocolate.
In addition to causing or intensifying headaches, caffeine can produce headaches if withdrawal from it occurs after an individual has become dependent on it. We believe that when there is a background of consuming an overabundance of caffeine during the day, some morning headaches are withdrawal headaches, created by withdrawal of caffeine during the eight or more hours of sleep. If you abuse caffeine (the term “abuse” is appropriate because caffeine is a drug) and if you have headaches, you might get substantial relief by gradually reducing your total caffeine consumption.

*68\88\2*