Lipitor is a medication used to lower cholesterol levels in the blood. According to Drug Patent Watch [1], the patent for Lipitor expired on November 30, 2011. However, this does not necessarily mean that all Lipitor pills produced before this date have expired.

The expiration date on a medication indicates the date until which the drug is guaranteed to be effective and safe to use. However, the Harvard Health Publishing [2] suggests that most drugs are still safe and effective to use even after their expiration date has passed. The expiration date is usually set by the manufacturer and is based on the drug's stability, potency, and purity.

The Scientist [3] notes that when a drug's patent expires, other manufacturers can produce generic versions of the drug. These generic versions are often less expensive than the brand-name drug, but they are required to meet the same safety and efficacy standards as the brand-name drug.

In conclusion, the patent for Lipitor expired in 2011, but the expiration date on individual pills may vary. While the expiration date indicates the date until which the drug is guaranteed to be effective and safe to use, most drugs are still safe and effective to use even after their expiration date has passed. Additionally, generic versions of Lipitor are now available.

Sources:
[1] https://www.drugpatentwatch.com/p/tradename/LIPITOR
[2] https://www.health.harvard.edu/staying-healthy/drug-expiration-dates-do-they-mean-anything
[3] https://www.the-scientist.com/the-nutshell/lipitor-patent-expires-41658