Lipitor (atorvastatin) is a medication used to lower cholesterol levels in the blood [1]. Antihistamines are a class of drugs used to treat allergic reactions and relieve symptoms such as itching, sneezing, and runny nose. There is no direct interaction between Lipitor and antihistamines. However, some antihistamines such as diphenhydramine can cause nightmares and disturbing dreams, which may affect sleep quality [2]. Lipitor itself is not known to cause nightmares or disturbing dreams.

It is worth noting that grapefruit juice can interact with Lipitor and increase the risk of side effects. Grapefruit juice contains compounds that can inhibit the enzyme responsible for breaking down Lipitor in the body, leading to higher levels of the drug in the blood. This can increase the risk of side effects such as muscle pain and liver damage [3]. Therefore, it is advisable to avoid grapefruit juice while taking Lipitor.

In conclusion, Lipitor does not affect the effectiveness of antihistamines. However, some antihistamines can cause nightmares and disturbing dreams, which may affect sleep quality. Grapefruit juice can interact with Lipitor and increase the risk of side effects. It is advisable to avoid grapefruit juice while taking Lipitor.

Sources:
[1] https://www.drugpatentwatch.com/p/tradename/LIPITOR
[2] https://www.goodrx.com/drugs/side-effects/medications-that-cause-nightmares-and-disturbing-dreams
[3] https://www.fda.gov/consumers/consumer-updates/grapefruit-juice-and-some-drugs-dont-mix