direct compression

Direct compression is the simplest way to make a tablet: just blend the dry powders and press them — no granulation step at all. It is the difference between baking a cake from a ready-mixed flour and mixing every ingredient from scratch; here you skip the messy in-between and go straight to the press.

It works only when the powder blend already flows well and compacts well on its own. To achieve that, formulators rely on special directly-compressible grades of excipients, such as spray-dried lactose or microcrystalline cellulose, which are engineered to flow and bind. The drug is simply mixed with these fillers, a disintegrant, a glidant and a lubricant, then fed to the tablet press.

The appeal is fewer steps, lower cost, less equipment, and no water or heat to harm sensitive drugs. The limits are real: high-dose drugs with poor flow or poor compactibility may overwhelm the excipients, and large dilute blends can separate (segregate), causing uneven drug content. In those cases granulation is chosen instead.