“Do you have to drink barium for a CT scan without contrast?”

 
 
The correct answer is “sometimes. “
 
Obviously, contrast that your drink ends up in your bowels. If the CT scan includes an area of your body that has bowel, this can be useful. If the CT scan is of your head, then oral contrast has no use.
 
In addition, it depends what the doctor is looking for, on the CT. A hernia? Oral contrast is very helpful. Lymph nodes? Oral contrast is very helpful. Kidney stone? Not so helpful. The whole thing is fairly complicated. There is no single answer. It all depends on the type of scan, part of body involved, and the pathology suspected.
 
Your doctor will order a CT scan with, or without IV contrast. Also with, or without oral contrast. If you lack confidence in your doctors ability to order the correct study, you should seek a second opinion. 

Depending on the reason for the exam or situation you don’t have to drink contrast before a ct scan. For example, no need for oral contrast if you can’t hold down anything or a ct test for renal stones.

However, it wouldn’t hurt to take oral contrast before a ct scan as it would improve the ability to find incidental gastrointestinal findings or true lesions within the bowel like tumors or polyps. It could also help delineate bowel from other adjacent normal or abnormal structures.