PQQ (Pyrroloquinoline Quinone) is an approved multi-functional supplement in Canada for health maintenance and in the United States as a dietary supplement for human consumption. 

PQQ is ubiquitous in the natural world. Its presence in interstellar stardust has led some experts to hypothesize a pivotal role for PQQ in the evolution of life on Earth. It has been found in all plant species tested to date. Neither humans nor the bacteria that colonize the human digestive tract have demonstrated the ability to synthesize it. This has led researchers to classify PQQ as an essential micronutrient.

The most widely used commercial product is pyrroloquinoline quinone disodium (PQQ·Na₂) salt. PQQ Na₂ is generally used in various experiments due to its high solubility in water, which makes it easy to handle, and this property gives PQQ·Na₂ an advantage in comparison with free-form PQQ.