Which drug can potentially cause increased levels of serotonin if combined with carbidopa-levodopa?

The correct answer involves the interaction of carbidopa-levodopa with monoamine oxidase A inhibitors. Carbidopa-levodopa is primarily used to treat Parkinson's disease by increasing dopamine levels in the brain. However, when combined with a monoamine oxidase A inhibitor, there is a risk of excessive serotonin levels because this type of inhibitor blocks the breakdown of serotonin in addition to other monoamines, leading to the potential for serotonin syndrome if serotonergic agents are present.

Monoamine oxidase B inhibitors, on the other hand, primarily affect dopamine metabolism without significantly impacting serotonin levels. Tricyclic antidepressants and SSRIs do influence serotonin levels, but they are not focused on the degradation pathway as monoamine oxidase A inhibitors are. Therefore, the combination of carbidopa-levodopa with a monoamine oxidase A inhibitor is particularly concerning regarding serotonin levels, establishing this combination as a potential risk for adverse effects related to increased serotonin.