In children… may apply to adults as well.
In any case, both inositol (a type of B vitamin) and fish oil are pretty safe to use.
Summary:
The bottom line of their small pilot study: fish oil plus inositol was significantly better than fish oil alone, which was superior to inositol alone in most primary outcomes. The sample was small, the dropout rate was nearly 50%, and the children were only moderately symptomatic, so conclusions are limited. However, the results quite strongly suggest that adding inositol to fish oil makes the omega-3s work better.
What dosages? In fish oil studies in adults, doses have been quite variable, but an important meta-analysis suggests that there is a threshold for efficacy. Few studies of fish oil for depression found it better than placebo if the dose was less than 1 gram of eicosapentaenoic acid (EPA) per day and—critically—the composition was at least 60% EPA (ie, EPA/EPA plus docosahexaenoic acid [DHA]). If anything, the EPA content relative to DHA was more important than its total dose: 2 studies that used lower doses but over 60% EPA had positive results.10
In the new study by Biederman’s group, all participants received the same dose of 975 mg of EPA per day regardless of their weight, using a version that was 59.1% EPA. Although there was no placebo arm in this study to determine whether 59% EPA at that dose was actually better than placebo, it was statistically better than inositol, which served as a so-called “active comparator” in lieu of a placebo—an ethical decision in this study population. The dose of inositol was roughly 80 mg/kg, for doses of 1500 to 2000 mg/d.
http://www.psychiatrictimes.com/bipolar-disorder/fish-oil-bipolar-disorder-children