• bipolar disorder
• immediate-release lithium
• prolonged-release lithium
• therapeutic adherence.
• tolerability

Lithium has been the gold standard in the treatment of bipolar disorder for several decades. Nonetheless, there has been a declining trend in lithium prescription in recent years, this is at least in part explained by matters of tolerability and therapeutic adherence. Extended-release formulations of lithium guarantee potential advantages over IR formulations in terms of tolerability and simpler therapeutical regimens, but comparative studies are at the present moment rather limited. The current study aimed at comparing treatment adherence, lithium levels and side effects of PR and IR formulations in patients receiving lithium for the first time, during a 1-year follow-up. At baseline evaluation a detailed anamnesis was collected and diagnosis of bipolar disorder was made based on DSM-5 criteria. The baseline sample included a total of 135 patients, 71 patients (53%) were prescribed PR lithium and 64 (47%) IR formulations. At the final evaluation the sample was composed by 83 individuals, 44 of them on PR lithium and 39 on immediate-release lithium salts. During follow-up, information was gathered on side effects and therapeutic adherence. While adherence was evaluated with the instrument of BARS scale, adverse events were registered based on patients’ complaints and clinical observation. Serum levels of lithium, creatinine and TSH were routinely monitored. Our study was consistent with previous trials on the topic and reported more stable lithium serum levels, superior tolerability and improved therapeutic adherence with PR formulations. More long-term studies are certainly needed.