Lipitor (atorvastatin) is a medication used to lower cholesterol levels in the blood. Dosage adjustments are made to achieve optimal cholesterol-lowering effects while minimizing the risk of side effects. According to the provided sources, it can take several weeks for a dosage adjustment to take effect.

The drug patent watch [1] states that the maximum recommended dose of Lipitor is 80 mg per day. The dosage can be adjusted based on the patient's response to treatment and the presence of side effects. Medscape [2] recommends that the initial dose of Lipitor is 10-20 mg per day, with a maximum dose of 80 mg per day. The dose can be increased every 2-4 weeks, depending on the patient's response and tolerance.

The FDA [3] states that the cholesterol-lowering effects of Lipitor can be seen within 2 weeks of starting treatment. However, the full effect may take up to 4 weeks. Therefore, it can take up to 4 weeks for a dosage adjustment to take effect.

In conclusion, it can take up to 4 weeks for a dosage adjustment of Lipitor to take effect. The initial dose is usually 10-20 mg per day, with a maximum dose of 80 mg per day. Dosage adjustments are made based on the patient's response to treatment and the presence of side effects.

Sources:
[1] https://www.drugpatentwatch.com/p/tradename/LIPITOR
[2] https://reference.medscape.com/drug/lipitor-atorvaliq-atorvastatin-342446
[3] https://www.fda.gov/media/155050/download