Relevance of analgesic abuse in the maintenance of chronic headaches

The mechanisms facilitating or prompting the chronicization of headache and the increased use of analgesics are still unknown and under debate. It is not clear whether the daily use of analgesics in chronic headaches is to be considered a habit or a therapeutic need. Recently, our group showed that items more involved in chronicization of headaches were the onset as migraine and the use of analgesics, namely mixture compounds. One of the most important features in inducing habit behavior is the reward: in this illness, does the reward come from the pain relief or from the intrinsic euphoric activity of the drugs, or does it depend on a more complex behavior? Although the system of neurotransmitters involved in the biology of reward is complex, at least four neurotransmitters are known to be involved at several sites in the brain: serotonin in the hypothalamus, the enkephalins (opioid peptides) in the ventral tegmental area, DOPA in nucleus accumbens, and the inhibitory neurotransmitter GABA in the ventral tegmental area and the nucleus accumbens. In a normal person, these neurotransmitters work together in a cascade of excitation or inhibition between complex stimuli and complex responses leading to a feeling of well being, the ultimate reward. In the cascade theory of reward, a disruption of these intercellular interactions results in anxiety, anger and other “bad feelings” or in a craving for a substance that alleviates these negative emotions. Probably, serotonin plays a pivotal role in migrane pathogenesis, thus drugs alleviating migraine should act through this neurotransmitter. Therefore, these drugs when used in specific settings, as compulsive behavior, may contribute to the development of mechanisms of reward linked to its use and may induce habit behavior. Epidemiological studies support this idea. The chronic use of barbiturate- or opiatecontaining analgesics is preferred by patients who daily consume drugs and who suffer from daily headaches.