Lipitor is a brand name for the drug atorvastatin, which is used to lower cholesterol levels in the blood. According to Drug Patent Watch , the most common side effects of Lipitor are headache, diarrhea, and upper respiratory tract infection. However, the website notes that these side effects are generally mild and go away on their own.
Mayo Clinic  provides a more comprehensive list of potential side effects of atorvastatin, including muscle pain or weakness, joint pain, and nausea. The website also notes that in rare cases, atorvastatin can cause a serious condition called rhabdomyolysis, which is the breakdown of muscle tissue that can lead to kidney damage.
The NHS  also lists muscle pain and weakness as common side effects of atorvastatin, but notes that these side effects usually go away once the medication is stopped. The website also lists other potential side effects, including digestive problems, sleep disturbances, and skin rash.
It's important to note that while these side effects are possible, not everyone who takes atorvastatin will experience them. Additionally, some people may experience side effects that are not listed here. If you are taking atorvastatin and experience any concerning side effects, it's important to speak with your doctor.