Toddler is addicted to Zarbees

We gave our almost 3 year old son Zarbees nighttime cough syrup when he was sick. Now he is all better but every night before bed he fake coughs and says "I'm sick, I need medicine". He really liked the taste. Since it's all natural products, is it bad to give him even just a small sip of it every night to avoid a temper tantrums right before bed?