It’s no fun to wake up with a hangover—especially without prior alcohol.
HEALTH You know that feeling you get: butterflies in the stomach; pressure on one side of the head or behind an eye; the inability to walk in a straight line, hold your head erect or concentrate; with no appetite, all you can do is stay in bed and try to sleep it off.
I'm not describing love sickness or a hangover. It's much like vertiginous migraine with a specific trigger—caffeine.
Here's where it gets interesting. Much as a drug addict craves the feeling of detachment from anxiety or responsibility, a person with chronic vertigo or migraines may be drawn to caffeine products even after realizing the outcome. In effect, an individual gets 'high' on caffeine.
The Chemical Process
Though dosage varies, caffeine can affect the human body in the same way as nicotine and cocaine. Taken in sufficiently small doses, these methylxanthines, or plant alkaloids, alter the function of the nervous system. The human body can adapt to the neurotoxic alkaloids, continuing to work, seemingly unaffected, despite interference. It does so simply by increasing production of indigenous adenosine (a-DEN-oh-seen).
Such adaptation, however, can result in painful withdrawal headaches during cessation or resumption as neurochemicals readjust. In the absence of caffeine, a regular user is oversensitive to adenosine and undersensitive to excitatory neurotransmitters. A caffeine user adapts to caffeine exposure but not to its deficiency. 
Although caffeine fulfills some of the criteria for drug dependence and shares with amphetamine and cocaine a certain specificity of action on the cerebral dopaminergic system, it does not act on the dopaminergic structures related to reward, motivation, and addiction.  Cafeine also depletes the absorption of fluids. With dehydration as the common denominator, caffeine intolerance can mimic symptoms of hangover.
|Caffeine and Adenosine Molecules|
Molecular diagrams of caffeine (left) and adenosine, 
6-amino-9-β-D-ribofuranosyl-9-H-purine (right). 
The molecularly similar shape of caffeine allows it to fit into and block adenosine receptors embedded in the surface membranes of neurons. Adenosine is a neuromodular that regulates serotonin, norepinephrine, dopamine, and acetycholine. Neurologists or psychologists might, therefore, treat migraines with serotonin and norepinephrine uptake inhibitors, also prescribed as antidepressants. Interestingly, dizziness and headache are included in the list of possible side effects. High doses of caffeine induce negative effects such as anxiety, restlessness, insomnia, and tachycardia. Adenosine supplements may be prescribed to treat supraventricular tachycardia (irregular heartbeat) or off-label conditions. [1-5]
Depending upon where it's located, adenosine functions as a tranquilizer, painkiller, or even pain inducer. By blocking adenosine, caffeine reverses the effect, causing pain where it is normally suppressed and exciting neurochemicals that should be tranquilized. Adenosine is a vasodilator, which can bring on peripheral pain. When blood volume is reduced, less oxygen reaches the brain, triggering migraines. Caffeine is also a vasodilator, constricting oxygen-carrying arteries.
Understanding how caffeine interacts with adenosine, provides rationale for the use of caffeine in migraine-formula pain killers. The goal is to block and reverse the cause of pain. This creates a conundrum if the migraine is caused by caffeine in the first place.
A high caffeine dosage is considered to be 250-500 mg (3-6 cups of coffee).  Consumption of 500-1000 mg can be life-threatening. But a so-called high dose varies between individuals as neurochemicals become deregulated. Sometimes people who formally consumed relatively high amounts of caffeine can develop a sensitivity after a period of abstinence. Neurotransmitters malfunction, and those malfunctions generate migraine symptoms.
A shortage of serotonin receptor activation prevents serotonin from appropriately blocking pain. A shortage of acetylcholine, a neurotransmitter essential to vision, in the retinas may cause the visual disturbances associated with migraine. A dopamine shortfall may cause the emotional and behavioral effects associated with migraine. A norepinephrine shortage causes the symptoms of sympathetic hypofunction associated with primary headache.
Why Caffeine May Be Ignored As Causative Agent
The news is not all bleak for caffeine. It is a potent stimulant that may increase productivity. Coffee contains niacin and antioxidants; it has been associated with a lower risk of type 2 diabetes and may be used as prophylactic for cardiovascular disease. Green tea protects against various cancers.
Practically everyone drinks coffee in the morning. Caffeine-packed energy drinks are consumed throughout the day. Caffeine is found in green tea, chocolate, and cola soft drinks. A 2005 survey study of the U.S. general population in which 87 percent of 18,081 subjects reported dietary caffeine intake and 71 percent said they drank coffee. [1,5,6] With such widespread use, most people—including some physicians—find it difficult to believe that caffeine could be causing migraines and disequilibrium in select patients, while others consuming higher doses appear unaffected. Migraines can be hereditary or an underlying psychosis may be suspected.
There can be several migraine exacerbators; some only trigger a reaction when combined with another, for example, caffeine and stress or chocolate with nuts. It is wise to first check with your doctor to rule out other causes for chronic headaches such as tumors and aneurisms. Blood tests can identify food allergies. A way to personally determine if you have a caffeine sensitivity (or addiction) is to pick a time when you have a few of days off from work and go "cold turkey for a day or two." Stop consuming caffeine; drink water or perhaps a natural juice cleanse if approved by your health care provider and follow with probiotics. There may be some withdrawal symptoms for a couple of days. Cessation may even cause migraines.
You may find that you are not addicted and can function well without caffeine. In some cases you may need to wean yourself off with tea. After abstinence for 90 days or longer, find another appropriate time when mental acuity may not be required. (Perhaps a holiday weekend.) Drink two 16 oz glasses of iced tea or two 8 oz cups of coffee and see how you feel the next couple of days. If there is no effect with two servings, pick different weekend and try four servings. If you experience some of the symptoms described at the beginning of this article, you will have learned your trigger. Because caffeine may be present in other foodstuffs, the tolerance level is not an exact science. Endeavor to stay far beneath your personal limit or eliminate caffeine completely from your diet.
You may later discover that intolerance is reliant upon a secondary factor or a completly different trigger; this can make you doubt your initial conclusions. Be patient and keep a journal to discuss findings with your healthcare provider.
- Caffeine and Migraine. Barry Spencer, caffeinandmigraine.com
- Depression (major depression). mayoclinic.com
- Neurologic Effects of Caffeine. medscape.com
- Adenosine. drugs.com
- Caffeine Toxicity. medscape.com
- Clinical Pharmacology of Caffeine. Benowitz NL. Annu. Rev. Med.
1990. 41:277-288. AnnualReviews.org
- Migraine Headaches. ihateheadaches.org