Classified as an anthraquinone, it can be isolated from rhubarb, buckthorn, and Japanese knotweed (Reynoutria japonica syn.

[2] Emodin is particularly abundant in the roots of the Chinese rhubarb (Rheum palmatum), knotweed and knotgrass (Polygonum cuspidatum and Polygonum multiflorum) as well as Hawaii ‘au‘auko‘i cassia seeds or coffee weed (Semen cassia).

[3] It is specifically isolated from Rheum palmatum L.[4] It is also produced by many species of fungi, including members of the genera Aspergillus, Pyrenochaeta, and Pestalotiopsis, inter alia.

It has various actions including laxative, anticancer, antibacterial and antiinflammatory effects,[6][7][8] and has also been identified as having potential antiviral activity against coronaviruses such as SARS-CoV-2,[9][10] being one of the major active components of the antiviral TCM formulation Lianhua Qingwen.

[11][12] Emodin has been shown to inhibit the ion channel of protein 3a, which could play a role in the release of the virus from infected cells.