Lipitor is a brand name for the drug atorvastatin, which belongs to a group of medications called statins. It is used to treat high cholesterol and to reduce the risk of heart disease and stroke [1]. Lipitor works by blocking an enzyme in the liver that produces cholesterol. This results in lower levels of cholesterol in the blood [2].

According to the National Health Service (NHS), the most common side effect of atorvastatin is muscle pain or weakness [2]. However, this side effect is rare and usually goes away after stopping the medication. Other side effects of atorvastatin may include headache, nausea, diarrhea, and constipation. These side effects are generally mild and temporary [2].

The Mayo Clinic states that atorvastatin can lower LDL (bad) cholesterol levels by up to 60 percent [3]. This reduction in cholesterol levels can occur within two weeks of starting the medication [3]. However, the full effect of atorvastatin may take up to four weeks to be seen [2].

In conclusion, Lipitor (atorvastatin) is a medication used to treat high cholesterol and reduce the risk of heart disease and stroke. It works by blocking an enzyme in the liver that produces cholesterol, resulting in lower levels of cholesterol in the blood. The most common side effect of atorvastatin is muscle pain or weakness, but this side effect is rare and usually goes away after stopping the medication. Atorvastatin can lower LDL (bad) cholesterol levels by up to 60 percent, and this reduction can occur within two weeks of starting the medication [2][3].

Sources:
[1] https://www.drugpatentwatch.com/p/tradename/LIPITOR
[2] https://www.nhs.uk/medicines/atorvastatin/side-effects-of-atorvastatin/
[3] https://www.mayoclinic.org/diseases-conditions/high-blood-cholesterol/in-depth/statin-side-effects/art-20046013