I am on Belladonn/Phenobarb (Donnetal). It was first prescribed as needed, but after I saw an associate of my doctor who is researching IBS extensively he told me it is best taken 4x a day. I babysit an infant, and explained to him that I feel uncomfortable being responsible for an infant while on a barbituate, so he said to at least take it every night at bedtime. I have been on other IBS meds, and find the Donnetal to be the most effective thus far. Taking it at bedtime has eliminated my getting up 5+ times a night to visit the restroom. Because it contains phenobarbitol, which is a barbituate, you will get drowsy. On a side note, my doctor said to never exceed the dosage because barbituates can be addicting, like most meds for pain.
Take care and be well