Based on the information available, Lipitor (atorvastatin) typically begins to lower cholesterol levels within 2 weeks of starting the medication [1]. However, it may take up to 4-6 weeks to see the full effects of Lipitor on cholesterol levels [2][3]. It's important to note that Lipitor's effectiveness can vary from person to person, and it may take longer for some individuals to see a reduction in their cholesterol levels [1].

It's also worth mentioning that Lipitor is a prescription medication used to treat high cholesterol and reduce the risk of heart attack and stroke [1]. Lipitor works by blocking an enzyme in the body that is needed to make cholesterol [1].

In addition, it's important to follow a heart-healthy lifestyle while taking Lipitor, including a healthy diet, regular exercise, and avoiding tobacco use [1].

Sources:

* [1] Mayo Clinic. Lipitor (Atorvastatin). <https://www.mayoclinic.org/drugs-supplements/lipitor-oral-route/description/drg-20063051>.
* [2] Drugs.com. Lipitor. <https://www.drugs.com/lipitor.html>.
* [3] DrugPatentWatch.com. Lipitor (Atorvastatin). <https://www.drugpatentwatch.com/drugs/lipitor>.