Lipitor is a drug used to lower cholesterol levels in the blood. According to drugpatentwatch.com [1], the active ingredient in Lipitor is atorvastatin calcium, which works by inhibiting an enzyme called HMG-CoA reductase that is involved in the production of cholesterol in the liver. The drug is usually taken once a day, and there has been some discussion about whether taking it at night might be more effective than taking it during the day.

A study published in the Journal of Clinical Lipidology [3] found that taking Lipitor at night was more effective than taking it in the morning. The study involved 51 patients with high cholesterol levels who were divided into two groups. One group took Lipitor at night, and the other group took it in the morning. After eight weeks, the group that took the drug at night had significantly lower levels of LDL cholesterol (the "bad" cholesterol) than the group that took it in the morning.

The reason why Lipitor might be more effective at night is not entirely clear. One theory is that the body produces more cholesterol at night, so taking the drug at that time might be more effective at reducing cholesterol levels [2]. Another theory is that the drug might be better absorbed when taken at night, although more research is needed to confirm this.

In conclusion, Lipitor is a drug used to lower cholesterol levels in the blood, and it is usually taken once a day. While there is some evidence to suggest that taking the drug at night might be more effective than taking it during the day, the reason for this is not entirely clear. More research is needed to determine why Lipitor might be more effective at night and whether this is a significant factor in its overall effectiveness.

Sources:
[1] https://www.drugpatentwatch.com/p/tradename/LIPITOR
[2] https://www.drugs.com/medical-answers/does-lipitor-work-better-if-you-take-it-at-night-416127/
[3] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC214096/