Aspirin: Watch the expiration date!
Jul 27, 2000
We often use medications well past the expiration date. We assume that the medication may lose potency but will still assist in easing our pain or lowering a fever. In the cause of aspirin, it may be doing much more than lowering a fever.
Since the 18th century, scientists have known that aspirin products extracted from willow bark would relieve pain and reduce inflammation. Throughout the centuries, medicine has refined the product we now take as aspirin. The compound is acetylsalicylic acid.
Originally, we ingested salicylic acid to relieve our pain. In addition to relieving our pain, it often damaged the mucous membranes of the mouth and esophagus and caused hemorrhaging of the stomach lining.
Scientists at Bayer realizes that the phenol group on the salicylic acid was causing the harm. By modifying the functional group, a safer product could be synthesized in the form of acetylsalicylic acid. This is the commercial product we use today. Simply, the salicylic acid was converted to acetylsalicylic acid.
However, as time passes the aspirin (acetylsalicylic acid) can undergo decomposition. This decomposition results in the breakdown of the acid. The product reverts back to the salicylic acid which contains the harmful phenol group.
If you open your aspirin bottle and observe a vinegar-like odor. Your aspirin, acetylsalicylic acid, has broken down into salicylic acid and acetic acid. The phenol group is present and can cause irritation to your stomach lining. This may occur in very old bottles that have exceeded the expiration date.
While you would not expect severe reactions to the expired aspirin, you might experience stomach irritation. Be safe and discard any old bottles of aspirin. This is one example of the importance of expiration dates.
Disclaimer: The author of this article does have a Ph.D. in chemistry. First, she is pleased that you read the entire article and made it through all of the chemical formulas and terminology. Second, she wishes the reader to understand this article is not medical advice but is a discussion on the scientific facts surrounding aspirin.