Natural products are compounds produced by living organisms whereas synthetic compounds originate from chemical synthesis and semi-synthetic compounds are derived from natural products by incorporating synthetic components in their molecular structure.

Many antibiotics are natural products that are extracted for example from bacteria or fungi (see natural products). In comparison, synthetic compounds are synthesized in a laboratory. In semi-synthesis, a part of the compound originates from nature for which further synthetic steps can be done to, for example, improve its properties.