A researcher from the University of California at San Diego reported at the American Heart Association meeting that simvastatin (Zocor®) can cause patients to develop sleep disturbances. It seems that the lipophilicity of the drug is relevant. Lipophilicity refers to the ability of a chemical compound to dissolve in fats, oils, and lipids. A class of drugs with similar actions may have members with different lipophilicity. With the statins, simvastatin is the most lipophilic, pravastatin (Pravacol®) the most hydrophilic - i.e. dissolving in water and similar liquids - rosuvastatin (Crestor®) may be hydrophilic, and atorvastatin (Lipitor®) is considered to be intermediate. Lipophilic drugs can cross the blood-brain barrier more easily, and therefore produce side effects such as sleep problems.

The researchers did a double-blind trial in 1000 men and postmenopausal women, who were randomized to take modest doses of pravastatin (Pravachol®), simvastatin, or a placebo for 6 months. Sleep quality and sleep problems were similar in all three groups at baseline. After 6 months, sleep quality was 'above average' with pravastatin and placebo, whereas it was below average with simvastatin. Sleep problems worsened during treatment to a greater extent with simvastatin than in the other two groups; it was linked to tiredness and irritability

These are not considered serious side effects. However, if someone is taking a statin and having such problems, their doctor can switch them to a more hydrophilic agent with the same benefits on lipids but less likelihood of getting into the brain.