Lipitor is a medication used to lower cholesterol levels in the blood, specifically low-density lipoprotein (LDL) cholesterol, which is commonly referred to as "bad" cholesterol. Lipitor's active ingredient is atorvastatin, which works by inhibiting an enzyme in the liver that is responsible for producing cholesterol [1]. According to a study published in the Journal of Clinical Lipidology, atorvastatin was found to significantly reduce LDL cholesterol levels by an average of 38.6% [2]. Additionally, a study published in Arteriosclerosis, Thrombosis, and Vascular Biology found that atorvastatin was effective in reducing LDL cholesterol levels in patients with familial hypercholesterolemia, a genetic disorder that causes high cholesterol levels [3].

In conclusion, Lipitor's active ingredient atorvastatin is effective in reducing LDL cholesterol levels in the blood. The medication has been found to significantly reduce LDL cholesterol levels by an average of 38.6% and has also been shown to be effective in patients with familial hypercholesterolemia.

Sources:
[1] https://www.drugpatentwatch.com/p/tradename/LIPITOR
[2] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2681027/
[3] https://www.ahajournals.org/doi/full/10.1161/01.atv.15.5.678