Image by Don W. Pottle

This is an image of crystals of aspirin with caffeine.   An Excedrin tablet was crushed in water and allowed to dissolve.   Drops of the solution were placed on a glass microscope slide and allowed to dry.  Examining and photographing the resulting crystals using a  60X oil immersion lens and DIC  (Differential Interference Contrast) filters produced these spindle-like images.  The spindles are aspirin crystals and the “rounded” crystal in the middle is caffeine.  No stains were used; the crystals naturally refract white light, causing the “rainbow effect.”

Aspirin works to relieve pain by inhibiting an enzyme (COX-2) that makes prostaglandins. At sites of pain, prostaglandins act to amplify pain signals at nerve endings, so blocking their production in turn helps block nociception (transmission of pain signals to the brain). Caffeine is a common adjuvant to analgesics that works through a different mechanism. Adenosine is a molecule with a complex role in nociception, and caffeine binds the same receptors on nerves that Adenosine binds. The difference is that caffiene blocks transmission of signals, whereas Adenosine enhances the signal.  Combining the two different ways that Aspirin and caffeine block nociception has an overall stronger analgesic effect.

To read more about Aspirin, caffiene, and pain medications, click the links below.

http://health.howstuffworks.com/medicine/medication/aspirin2.htm

http://cafeesaude.com/wp-content/uploads/2012/01/Dor-J-Sawynok-Pain-Volume-152-2011.pdf

http://www.health.harvard.edu/pain/12-things-you-should-know-about-pain-relievers