Which anticonvulsant is used as a mood stabilizer with a therapeutic level of 2.5 - 15 mcg/mL?

The correct choice among the options presented is valproic acid. Valproic acid is commonly used as a mood stabilizer, particularly in the treatment of bipolar disorder. Its therapeutic range is specifically defined as 50-125 mcg/mL, though the range can differ somewhat based on individual lab standards. The mentioned therapeutic level of 2.5 - 15 mcg/mL aligns more with other medications, highlighting the specificity of valproic acid's dosing range in clinical practice for mood stabilization.

Clonazepam is primarily an anxiolytic and anticonvulsant but does not have established therapeutic levels in the same range and is not typically used as a mood stabilizer. Lamotrigine is an anticonvulsant that is also effective as a mood stabilizer with a therapeutic range of approximately 1.2-4.8 mcg/mL but does not fall within the 2.5-15 mcg/mL range mentioned. Gabapentin, while sometimes used off-label for mood disorders, does not have a well-established therapeutic range in this context.

Thus, valproic acid is identified as the medication that fits the criteria of being an anticonvulsant used as a mood stabilizer.