Why is methylcellulose used in pharmaceuticals?
Methyl cellulose is a dry binder. It is used to make a pill with a small mass of active ingredient and as much binder as required to make the pill a manageable size.

The following properties make methyl cellulose a good dry binder:


inexpensive
non-allergic
vegetarian
soluble in cold water
non-digestable
nontoxic


Most of this information is from the Wikipedia article.