Based on the information provided, I can tell you that Lipitor (atorvastatin) is a medication used to lower cholesterol levels. According to the American Heart Association [1], statins like Lipitor can reduce LDL (bad) cholesterol by 20% to 60%. However, the exact amount of cholesterol reduction can vary depending on the individual's initial cholesterol level, the dose of Lipitor prescribed, and other factors. WebMD notes that some people may see a reduction in LDL cholesterol levels within four to six weeks of starting Lipitor, but it can take up to six months to see the full effect [3]. It's important to note that Lipitor is most effective when used in conjunction with a heart-healthy lifestyle, including a healthy diet, regular exercise, and avoiding tobacco use [2][3].

Sources:
[1] <https://www.ahajournals.org/doi/full/10.1161/01.atv.15.5.678>
[2] <https://www.webmd.com/cholesterol-management/features/when-your-doctor-orders-cholesterol-lowering-medications>
[3] <https://www.drugpatentwatch.com/p/tradename/LIPITOR>