Statins begin to have a noticeable effect after one week. For four to six weeks after statin treatment has started, cholesterol levels will gradually decrease until the drug has had its maximum effect. From that point, the effects of statin treatment will remain stable unless there is some other change, such as new medications or a drastic change in diet. As a result, statins can generally be used for long-term management of high cholesterol.
You also need to check your blood lipid levels to adjust your statin use.