Direct compression: Most manufacturers agree that direct compression is superior with few steps since it does not require much equipments and handling expenses as required for wet method of tablet manufacture. The medicaments with large doses having good bulk density, flowability and compressibility can be directly compressed.

There are few crystalline substances such as inorganic salts (e.g. NaCl, KCl, and KBr), which may be compressed directly with very few additives such as lubricants and glidants. However, sometimes these compressed tablets may not disintegrate in the given time limit, and hence, substances such as disintegrating agents are added.

The different stages involved are as follows:

1. Milling or size reduction
2. Blending
3. Compression

Advantages

1. Less amount of additives are used in the formulation.
2. Number of steps involved is minimum.
3. Less equipments are used.
4. Less time consuming.

Disadvantage

1. All medicaments cannot be compressed directly.

Requirements for direct compression

1. Dose of medicament or drug should be more.
2. The medicaments should have very good mechanical strength and cohesiveness.
3. Medicament should have very good compressibility and other derived properties such as bulk density, angle of repose, etc.

Slugging or double compression: This method is used for those drugs, which are sensitive to heat, moisture, or both. This method is also called as granulation by compression or double compression method. The various process steps involved are as follows:

1. Size reduction: In this step, the size of the drug is reduced and passed through sifter to get the desired particle size of the drug.
2. Mixing: In this step, drug along with additives that are compressible like dicalcium phosphate granules, which are prepared previously are mixed along with glidant and lubricant and punched or compressed into compact masses called slugs by using flat punches using high compression force using multi-station tablet compression machine.
3. Milling: In this step, slugs are size reduced by using multi mill and passed through sifter to get the desired granules.
4. Blending: The obtained granules are then blended with additives such as disintegrating agents, lubricants and glidants for sufficient period of time using double cone blender.
5. Compression: The lubricated granules are finally compressed into tablets of desired weight, hardness, and thickness using multi station tablet compression machine.