Lipitor, also known as atorvastatin, is a medication used to lower cholesterol levels in the blood and reduce the risk of heart disease and stroke. According to the National Health Service (NHS) [1], it may take up to four weeks to see the full effects of atorvastatin. However, some people may experience a reduction in cholesterol levels within two weeks of starting the medication. The amount of time it takes to see results may vary depending on the individual's condition and the dosage of the medication.

A study published in the American Heart Association journal [2] found that atorvastatin can significantly reduce LDL cholesterol levels within two weeks of starting treatment. The study also found that the maximum reduction in LDL cholesterol levels occurred after four weeks of treatment. The study suggests that patients who do not achieve their target cholesterol levels within four weeks may require a higher dose of atorvastatin or a different medication.

It is important to note that atorvastatin should be taken as prescribed by a healthcare professional. It is not recommended to stop taking the medication without consulting a doctor, even if cholesterol levels have improved. Additionally, lifestyle changes such as a healthy diet and regular exercise can also help to improve cholesterol levels and reduce the risk of heart disease and stroke.

Sources:
[1] NHS. Common questions about atorvastatin. https://www.nhs.uk/medicines/atorvastatin/common-questions-about-atorvastatin/
[2] American Heart Association. Time Course of LDL Cholesterol Lowering and Its Relationship to Drug Dosing in the Atorvastatin Atherosclerosis Regression Study. https://www.ahajournals.org/doi/full/10.1161/01.atv.15.5.678