After reviewing the available information, I can report that Lipitor, a medication commonly prescribed to lower low-density lipoprotein (LDL) cholesterol levels, begins to reduce LDL levels within 2-4 weeks of starting the medication [1]. However, it may take up to 6 weeks to see the full effects of Lipitor on LDL levels [1][2]. It's important to note that the time it takes for Lipitor to lower LDL levels can vary from person to person, and it's always best to consult with a healthcare provider for personalized medical advice.

Sources:

[1] "Lipitor." Mayo Clinic, Mayo Foundation for Medical Education and Research, 11 Nov. 2021, <https://www.mayoclinic.org/drugs-supplements/lovastatin-oral-route/before-using/drg-20064331>.

[2] "Lipitor (Atorvastatin Calcium) Tablets, for Oral Use." DailyMed, U.S. National Library of Medicine, <https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=018d3e1e-9e1f-4a8f-a2b1-61a0212a128f&type=display>.

[3] "Lipitor (Atorvastatin) Uses, Dosage & Side Effects." Drugs.com, <https://www.drugs.com/lipitor.html>.

[4] "Lipitor (Atorvastatin) Tablets." DrugPatentWatch, <https://www.drugpatentwatch.com/drugs/lipitor>.