Oral formulations
The way a drug is formulated can avoid some of the problems associated with oral administration.
Drugs are normally taken orally as tablets or capsules.
The drug (active substance) itself needs to be soluble in aqueous solution at a controlled rate. Such factors as particle size and crystal form can significantly affect dissolution. Fast dissolution is not always ideal. For example, slow dissolution rates can prolong the duration of action or avoid initial high plasma levels.

Tablet form
A tablet is usually a compressed preparation that contains:
5-10% of the drug (active substance);
80% of fillers, disintegrants, lubricants, glidants, and binders; and
10% of compounds which ensure easy disintegration, disaggregation, and dissolution of the tablet in the stomach or the intestine.
The disintegration time can be modified for a rapid effect or for sustained release.
Special coatings can make the tablet resistant to the stomach acids such that it only disintegrates in the duodenum as a result of enzyme action or alkaline pH.
Pills can be coated with sugar, varnish, or wax to diguise the taste.
Some tablets are designed with an osmotically active core, surrounded by an impermeable membrane with a pore in it. This allows the drug to percolate out from the tablet at a constant rate as the tablet moves through the digestive tract.

Capsule form
A capsule is a gelatinous envelope enclosing the active substance. Capsules can be designed to remain intact for some hours after ingestion in order to delay absorption. They may also contain a mixture of slow- and fast-release particles to produce rapid and sustained absorption in the same dose.