Any "anti-nausea" med "can" cause drowsiness. When I had mine, they gave me no such "anti-nausea" medication ... so I'm not quite sure why they think you would need it (the cocktail is basically tasteless). But, even if you do take it, believe me ... after each glass of the "cocktail", you probably won't have time to get sleepy from the medication before relieving yourself of the cocktail effluence.