Well so we already knew that drugs that increase serotonin levels decrease bone density over time. Medscape's new report says that osteoporosis is associated not just with SSRIs, but with benzos and some mood stabilizers other than lithium. Tricyclic antidepressants are protective for bones, but they have other gnarly side effects.

They've also found that mental disorders themselves have significant bone correlations. Dementia, schizophrenia and alcohol dependence are associated with reduced bone density. Depression is associated with less osteoporosis---which makes sense if you think that a lot of depression is due to low serotonin levels. Bipolar disorder and drugs other than alcohol were not found to have any correlation with osteoporosis.

Aside: FDA has released new warning that Tramadol (an opioid) increases suicide risk.