According to the information provided, the dosage of Lipitor, a medication used to treat high cholesterol, has been lowered. The exact reason for this change is not specified in the information given. However, it is mentioned that the U.S. Food and Drug Administration (FDA) has required a label change for Lipitor and other similar drugs, known as statins, due to the risk of increased blood sugar levels and memory loss [1]. This label change may have contributed to the decision to lower the dosage of Lipitor.

Additionally, it is noted that the patent for Lipitor has expired, which has led to the introduction of generic versions of the drug [2]. With the availability of generic alternatives, it is common for doctors to prescribe lower doses of brand-name drugs like Lipitor, as generic versions are typically less expensive [3].

In summary, while the exact reason for the lowering of Lipitor's dosage is not specified, it may be due to a label change required by the FDA and the availability of lower-cost generic alternatives.

Sources:
[1] <https://www.fda.gov/drugs/postmarket-drug-safety-information-patients-and-providers/statin-drugs-and-risk-increased-blood-sugar-and-memory-loss>
[2] <https://www.drugpatentwatch.com/lipitor-patent-expiration-date/>
[3] <https://www.webmd.com/cholesterol-management/news/20120326/lipitor-patent-expiration-what-it-means-for-you>