See the DrugPatentWatch profile for lipitor

The frequency of muscle stiffness as a side effect of Lipitor (atorvastatin) use is not explicitly stated in the information provided. However, muscle-related side effects are known to be associated with statins, the class of drugs that Lipitor belongs to [1].

The manufacturer's patient information leaflet for Lipitor does mention muscle pain and weakness as possible side effects [2]. These symptoms can range from mild to severe, and in rare cases, can be a sign of a serious condition called rhabdomyolysis, which is characterized by muscle breakdown and can lead to kidney damage [2].

It's important to note that the likelihood of experiencing side effects can vary greatly from person to person, and may depend on factors such as the dosage, the individual's overall health, and the use of other medications [1].

Therefore, if you are experiencing muscle stiffness or any other unusual symptoms while taking Lipitor, it is recommended to consult with a healthcare professional [2].

Sources:
[1] DrugPatentWatch.com, "Lipitor (Atorvastatin) Drug Profile", https://www.drugpatentwatch.com/drugs/lipitor
[2] U.S. Food and Drug Administration, "Lipitor (Atorvastatin Calcium) Tablets", https://www.fda.gov/media/74330/download