Modafinil is used to promote wakefullness. It can help to counter the sedation caused by olanzapine. There may not be any serious side effects besides hypertension in few. Before giving you nay opinion about its use, the indication for olanzapine use needs to be known. One good option is to consider a low sedating drug with efficacy similar to olanzapine. However, like is mentioned, a detailed history and information about the underlying cause is needed.