See the DrugPatentWatch profile for lipitor

Based on the information available, there is no specific data or studies indicating the rate at which Lipitor's effectiveness decreases after its expiration date. The effectiveness of a medication after its expiration date can vary depending on the drug's chemical composition and storage conditions [1].

The expiration date on a medication, such as Lipitor, indicates the date up to which the manufacturer guarantees the full potency and safety of the drug [1]. After this date, the medication's effectiveness may decrease, but it doesn't necessarily mean that it becomes ineffective immediately [1].

It's important to note that the U.S. Food and Drug Administration (FDA) has stated that most medications retain their full potency for a considerable period beyond their expiration dates [1]. However, the FDA does not have data on the efficacy of drugs past their expiration dates because it doesn't test drug expiration dates after approval [1].

In conclusion, while there is no specific information on how quickly Lipitor's effectiveness decreases after its expiration date, it's generally advised to use medications before their expiration dates to ensure their full potency and safety.

Sources:
[1] Drug Patent Watch. (n.d.). Expired Drugs: What You Should Know. Retrieved from <https://www.drugpatentwatch.com/expired-drugs-what-you-should-know/>