Lipitor is a medication that is used to lower cholesterol levels in the blood. According to Drug Patent Watch [1], Lipitor's active ingredient is atorvastatin calcium, and it works by inhibiting the production of cholesterol in the liver. The medication is known to have side effects, and one of them is insomnia or sleep disturbances [2]. However, it is not clear whether Lipitor can cause REM sleep disturbances.

A study published in the Journal of Clinical Sleep Medicine [3] found that statins, including atorvastatin (Lipitor), can affect sleep quality. The study involved 1,016 patients who were taking statins, and it found that statin use was associated with an increased risk of poor sleep quality, including difficulty falling asleep and staying asleep. However, the study did not specifically investigate the effect of statins on REM sleep.

Another study published in the Journal of Clinical Psychopharmacology [4] investigated the effects of atorvastatin on sleep in patients with major depressive disorder. The study found that atorvastatin did not significantly affect sleep architecture, including REM sleep.

In conclusion, Lipitor is known to cause sleep disturbances, including insomnia. However, there is limited research on whether Lipitor specifically causes REM sleep disturbances. Further research is needed to fully understand the effects of Lipitor on sleep architecture.

Sources:
[1] https://www.drugpatentwatch.com/p/tradename/LIPITOR
[2] https://www.aarp.org/health/drugs-supplements/info-04-2013/medications-that-can-cause-insomnia.html
[3] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2699168/
[4] https://pubmed.ncbi.nlm.nih.gov/23860328/