Small molecule drugs are made from chemicals, and are compounds of low molecular weight. Examples of small molecules are many of the drugs that you would find in your standard medicine cabinet, such as aspirin, Benadryl, or ibuprofen. These compounds tend to be easier to make, and lower cost than biologics.

Biologics are compounds that come from living sources, and are larger and more complex molecules. They’re produced via biotechnology in a living system such as plant or animal cells. There are many that are used as medications and are approved for use in the United States, including vaccines, drugs that treat inflammatory diseases such as Crohn’s or rheumatoid arthritis. Many of the compounds that we use for scientific purposes, such as antibodies, while they’re not considered medications, are also biologic compounds.

Small molecules are not obsolete though, and will always be easier to make and produce in large quantities, and be less expensive. They can also often easily cross the cell membrane due to their size, and target proteins that biologics might not be able to target. Both types of compounds have their own unique sets of characteristics that make them valuable for both scientific and clinical use.