Capsules are easier to swallow and are used by manufacturers when the drug cannot be compacted into a solid tablet. They are also useful when the drug needs to be mixed with oil or other liquid to aid absorption in the body. It is normally a shell or container made of gelatin that contains the drug.
There are two types of capsules, hard or soft.
Hard capsules, which are more commonly seen, are made up of a rigid shell in two pieces that fit together and is then filled with the drug. This formulation is normally more suitable for drug powders and can only be used if the drug will be easily dissolved in the stomach.
Soft capsules are formed in a single piece and are more suitable for oils e.g. Fish oils, or drugs that need to be dissolved in oils or other liquids to aid the drug to be absorbed in the stomach. In soft capsules, the drug is combined with an appropriate solvent in the centre of the capsule and the capsule shell melts within minutes in the stomach.
Drugs are easily absorbed from these mixtures offering two distinct advantages:
1) Quicker effect, which is good for immediate pain relief
2) Drug absorbed more effectively, so lower doses can be used which in turn means the soft capsules can be made smaller, making swallowing easier.