Lipitor, also known as atorvastatin, is a medication used to lower cholesterol levels in the blood. According to the British Heart Foundation [3], statins like Lipitor can start to lower cholesterol levels within two weeks of starting the medication. However, it may take up to four weeks to see a significant improvement in cholesterol levels [3]. The drug works by inhibiting the enzyme HMG-CoA reductase, which is responsible for producing cholesterol in the liver [2]. By reducing the production of cholesterol, Lipitor can help to lower LDL cholesterol levels and reduce the risk of heart disease [2]. It is important to note that the effectiveness of Lipitor may vary from person to person and depends on factors such as age, gender, and overall health [2]. Additionally, Lipitor should be taken as directed by a healthcare provider and should not be stopped or changed without consulting a doctor [1].

Sources:
[1] https://www.drugpatentwatch.com/p/tradename/LIPITOR
[2] https://www.ncbi.nlm.nih.gov/books/NBK548236/
[3] https://www.bhf.org.uk/informationsupport/heart-matters-magazine/medical/drug-cabinet/statins