Fiber - both soluble and insoluble - occurs naturally in plant foods.
If you can take a medication with food, you can typically take it with fiber.
If your medication must be taken on an empty stomach, don't take it with fiber any more than you would take it with food.
How to know the difference?
It depends on your specific medication. Does food interfere with its absorption? If yes, the bottle and your pharmacist will tell you to take it on an empty stomach.
Typically these medications are taken one hour before, or two hours after, your fiber and your food.
Can you take your medication with food? If yes, then food does not interfere with its absorption. Typically you can simply treat your IBS fiber supplement like food, and take it with the medication.
If foods that contain fiber don't affect medication absorption, a fiber supplement typically won't either.
But - it's not just about the type of fiber - it's about the type of medication.
Notice all these "typicallys"... Always ask your pharmacist if you can take your specific medication with your specific soluble fiber supplement. There are unique interactions that don't fit the general guidelines above.
Tip Takeaway: Treat fiber supplements like food. If your medication must be taken on an empty stomach, take it one hour before, or two hours after, your fiber supplement. If your medication can be taken with food, it can typically be taken with fiber. But always ask your pharmacist to be sure!