Individuals with bipolar and major depressive disorders have considerably higher suicide rates than the general population. However, estimating the risk of suicide is complicated, and there exists a general lack of consensus among researchers regarding whether suicide rates are higher in patients with unipolar, bipolar I, or bipolar II depressive disorders. Isolating the specific factors that contribute to the high risk of suicide in patients with affective disorders can be challenging as well; substance and alcohol abuse, family history of suicide, differences in allele distributions, comorbid anxiety, depression recurrence, seasonal effects, rapid cycling, and a history of hospitalizations for depression all appear to contribute to the likelihood that these patients will engage in suicidal behavior. Research does tend to agree that lithium is efficacious in decreasing suicidal behavior in patients with affective disorders.