Repeat steps 1 through 5 for every dose of benefiber you take. Also, take benefiber two hours before or after taking other medicines. Benefiber Prebiotic Sugar-free On The Go Fiber Supplement Powder - 28ct In this case, reduce or cease usage of benefiber and consult a doctor about the appropriate dose. How long does it take to get used to benefiber . Addiction medicine 53 years experience. Did you wonder how long you needed to take it? Do not use this fiber supplement if you have: I would suggest that it takes only 2 to 4 days for your body to get used to a high fiber diet. How long do benefiber products stay fresh? Benefiber is primarily used for preventing constipation. Side effects of benefiber may occur when too much is taken and include diarrhoea. If you are using the stick packs of benefiber, empty out one powder pack into 4 to 8 oz. Keep out of reach of children. Some users report regular bowel movements and less constipation with only one week of ...