Lipitor is a widely used medication for lowering cholesterol levels and reducing the risk of heart disease. The effectiveness of Lipitor is evaluated through various clinical trials and studies, which are conducted periodically to assess its safety and efficacy. According to the sources provided, Lipitor's effectiveness has been evaluated in several studies.

One study published in the Journal of Clinical Lipidology [2] analyzed the effectiveness of Lipitor in reducing LDL cholesterol levels in patients with hypercholesterolemia. The study concluded that Lipitor was effective in reducing LDL cholesterol levels and was well-tolerated by patients.

Another study published in the Reproductive Biology and Endocrinology journal [3] evaluated the effect of Lipitor on fertility in male rats. The study found that Lipitor had no significant effect on fertility in male rats.

Furthermore, the effectiveness of Lipitor is also evaluated through its patent status. According to Drug Patent Watch [1], the patent for Lipitor expired in 2011, which allowed for the development of generic versions of the drug. This indicates that Lipitor's effectiveness has been evaluated over a long period of time and that it has been deemed safe and effective for its intended use.

In conclusion, Lipitor's effectiveness is evaluated through various clinical trials and studies, which are conducted periodically to assess its safety and efficacy. These studies have shown that Lipitor is effective in reducing LDL cholesterol levels and is well-tolerated by patients. Additionally, the expiration of Lipitor's patent indicates that its effectiveness has been evaluated over a long period of time and has been deemed safe and effective for its intended use.

Sources:
[1] https://www.drugpatentwatch.com/p/tradename/LIPITOR
[2] https://pubmed.ncbi.nlm.nih.gov/25016482/
[3] https://rbej.biomedcentral.com/articles/10.1186/1477-7827-12-65