Why do antihistatmines make me sleepy?

Any allergy sufferer knows that histamine is the enemy.  Walk into a florists shop or into a basement filled with mold and your body is filled with more histamine than you know what to do with.  It sets off many an allergic reaction.  Before you reach for the benderyl or other antihistamine next time, maybe you should know a few other things about this little substance.

Histamine is a hormone made by the human body it has a number of functions including initiating the swelling response, initiation secretion of gastric acid, allowing fluid to seep through cell walls (hence a runny nose), also known as vasodialation.  What might be the most surprising though is that histamine is a neurotransmitter. Yes, histamine sends signals between the neurons in your brain.  Its especially concentrated in the hypothalamus, a small region in your brain that orchestrates most of the chemical balance in your body.

Other neurotransmitters used in conjunction with histamine are serotonin, and norepinephrine. Parts of the brain that actively use histamine control functions such as sleep, emotion, temperature, memory and emotion. 

Histamine is essential for waking--hence why antihistamines make you sleepy.  An antihistamine may make your nose feel better, but your also temporally shutting down one of the chemicals that helps your body stay alert.  However, taking antihistamines does not promote natural sleep.  In hypothalamus histamine is related to sleep, but is different that the other biological factors that influence deep and restful sleep, including your circadian rhythm and melatonin production.

For more news on this study see the link below:  http://www.news-medical.net/?id=5044

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