APIs are broadly categorised into two types – synthetic and natural. Synthetic APIs are further classified into innovative and generic synthetic APIs, based on the type of synthesis used. Synthetic chemical APIs, also known as small molecules, constitute a large part of the pharmaceutical market, with many small molecule drugs commercially available in the market. Natural APIs are used in making biologics, which are increasingly becoming the top-selling drugs in the market. Despite the growing demand, biologics are currently significantly fewer in number compared to small molecule drugs. Based on the solubility, APIs are categorised into insoluble and soluble drugs。