Loquat is most often used for
Eriobotrya japonica is the plant which bears the fruits we refer to as 'Loquat', or specifically the common or wild Loquat. While the fruits themselves are sold as a food product with no medicinal history, the seeds have been added to alcoholic drinks which are thought to promote longevity while the leaves have been ingested on an as-needed basis to treat cough, sputum, and throat inflammation associated with sickness.
The leaves themselves are a good source of triterpenoid molecules, with some unique ones including tormentic acid (and some variants) and euscaphic acid although the majority of these triterpenoids are just ursolic acid and a variety of methoxylated or polyhydroxylated variants. It seems to have a wider variety of triterpenoids rather than a high level of any one triterpenoid, and this class of molecules seems to underlie most of the benefits associated with the leaf extracts. There is not a good idea of what molecules are in the seeds, and it is though that they are also a source of triterpenoids since no unique molecules are known in them.
The benefits of this plant right now tend to be associated with either high or undisclosed doses of the seeds, suggesting that they probably don't apply to oral ingestion of standard doses in humans. The only roles where supplementation may be useful are in control of diabetes and possibly in reducing ulcer formation, but both of these claims can be achieved if not easily outperformed by using isolated ursolic acid or other supplements. There is not enough research into the variety of triterpenoid variations (the polyhydroxylated or methyoxylated variants) to know if they possess unique properties or not.
There is currently not enough information to recommend an ideal supplemental dose of this plant for any of its recommended supplemental purposes, although one study referencing the 'recommended human dose' for the seeds used a rat dose of 40mg/kg (ie. abouto 3-5g of the seeds for adults).