Psyllium must be taken with a significant amount of fluid, to prevent choking. This can be a problem on severely fluid-restricted diets. And it can interfere with the absorption of meds and minerals, if you take them together with psyllium.
An alternative is Unifiber. Unifiber doesn't need to be taken with fluid, though it can be mixed into foods or beverages too. And Unifiber is just cellulose, so it doesn't interact with meds you are taking.
http://www.unifiber.com/