Objectives. Many patients with bipolar disorder suffer from metabolic disorder. Lovastatin is effective for treating major depression. This double-blind randomized placebo controlled clinical trial investigates whether lovastatin is a useful adjuvant to lithium for treating mania. Methods. Fifty-four patients with bipolar disorder-manic phase were randomly allocated into lovastatin or placebo group. The clinical symptoms were assessed at baseline, week 2, and week 4 using Young Mania Rating Scale. Adverse effects were checked. Results. Forty-six out of 54 patients completed this trial. The mania score in the lovastatin group decreased from 40.6 (11.1) at baseline to 12.9 (8.7) and 4.1 (5.4) at weeks 2 and 4, respectively. The score in the placebo group decreased from 41.0 (11.2) at baseline to 12.8 (8.07) and 5.8 (4.6) at weeks 2 and 4, respectively. However, there was no significant difference between groups at week 2 and week 4. The adverse effects rates were comparable between the two groups. No serious adverse effect was found. Tremor and nausea were the most common adverse effects. Conclusions. Lovastatin neither exacerbated nor decreased the symptoms of mania in patients with bipolar disorder. Current results support that the combination of lovastatin with lithium is tolerated well in bipolar disorder. The trial was registered with the Iranian Clinical Trials Registry (IRCT201302203930N18).