Lipitor is a medication used to lower cholesterol levels in the blood. The active ingredient in Lipitor is atorvastatin calcium, which inhibits the enzyme responsible for producing cholesterol in the liver [1]. According to a study published in the National Library of Medicine, the absorption of atorvastatin calcium is not significantly affected by the intake of skim milk [2]. However, the FDA-approved label for Lipitor recommends taking it without regard to food, as food does decrease the absorption of atorvastatin calcium, and high-fat meals can further decrease its absorption [3]. Therefore, it is best to take Lipitor on an empty stomach or with a low-fat meal to ensure optimal absorption.

Sources:
[1] https://www.drugpatentwatch.com/p/tradename/LIPITOR
[2] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1312230/
[3] https://www.accessdata.fda.gov/drugsatfda_docs/label/2009/020702s056lbl.pdf