Hardy orange

The compound is named for the plant and is its most useful chemotaxonomic marker: an immature citrus fruit that is high in poncirin and low in neohesperidin is this species and not bitter orange. Preclinical work pairs it with naringin as the fraction carrying the anti-inflammatory and gut-directed activity, including in a mouse colitis model where the two together attenuated both colonic inflammation and the associated depressive-like behaviour.

Carries much of the bitterness and, with poncirin, much of the measured anti-inflammatory activity. Enzymatic deglycosylation matters here: treating the ethanol extract with naringinase, which cleaves naringin to naringenin, increases its anti-inflammatory effect in vitro, which is consistent with the aglycone rather than the glycoside being the active species after oral dosing.

Not important pharmacologically at these levels; important forensically. Two orders of magnitude separate this species from the bitter orange whose drug it is substituted for, so a neohesperidin assay identifies the substitution unambiguously where morphology may not. The same survey found this species also lacked hesperetin and tangeretin, which a 2022 review of the species does list among its constituents, so the absence is best read as a property of the market samples examined rather than a settled property of the plant.

This is the pharmacologically decisive difference between this species and bitter orange, and it runs in the reassuring direction. Synephrine is the sympathomimetic amine responsible for the blood pressure and heart rate concerns attached to Citrus aurantium preparations and to bitter orange weight-loss products. Because this species carries much less of it, the cardiovascular cautions written for Zhi Shi do not transfer to it at full strength. The corollary is less comfortable: a patient given this species when Zhi Shi was prescribed is receiving a drug with a materially different pharmacology, not simply a cheaper grade of the same one.

The class that governs this drug's interaction potential. Methoxsalen is 8-methoxypsoralen, the compound used clinically as a photosensitiser in PUVA therapy and, separately, as a research and clinical inhibitor of CYP2A6; imperatorin and isoimperatorin are also documented cytochrome P450 inhibitors. Whether the amounts delivered by a decoction of this fruit are enough to matter has not been measured, so the interaction risk is inferred from chemistry rather than observed, but the class is unambiguously present and psoralens are unambiguously phototoxic.

Widely studied for chemopreventive and anti-inflammatory activity in rodent models. It is not a psoralen and lacks the furan ring, so it does not carry the phototoxicity of the furanocoumarins above; its relevance here is mostly as a marker and as part of the argument that the coumarin fraction, not only the flavonoids, contributes to activity.

Accounts for the aromatic, carminative character of the drug. It is volatile and largely driven off by prolonged decoction, so preparations differ substantially in how much of it they deliver.

Responsible for part of the delayed bitterness of the immature fruit. Their contribution at decoction concentrations is unestablished; they are cited more often as novel chemistry than as demonstrated actives.

Li Shizhen gave gou ju its own entry expressly to separate it from zhi shi. He describes a thorny tree whose trunk and leaves resemble the tangerine's, white flowers with green centres and no scent in the third month, and fruit the size of a pellet, shaped like zhi shi but thin-rinded and unscented. He then records that households plant it as a hedge and that some gather the small fruits and sell them fraudulently as zhi shi and as qing pi, ending with the instruction that one must be able to tell them apart. The adulteration this database records as a modern quality-control finding is therefore a problem the tradition itself identified and named more than four centuries ago.

The earliest of the citrus monographs and the first text to say plainly that the zhi shi of Shangzhou was in fact this species rather than the genuine drug, substituted because true zhi shi was hard to obtain. It places the substitution four hundred years before Li Shizhen and shows it originated in scarcity rather than in deliberate fraud alone.

Records the variety popularly called chou ju, stinking orange, whose rind is faintly green and which the author says is unfit for medicinal use. He complains that market sellers gather the green-coated fruit to deceive buyers for profit, to no benefit and some harm, and directs that material entering medicine should be sought dark in colour. This is the origin of the trade name lu yi zhi shi, green-coat zhi shi, still used for material from this species.

Continues the same complaint into the Qing, noting that small fragrant pomelo fruits were being gathered in the sixth and seventh months to counterfeit zhi shi and zhi qiao, and that this species was likewise used. Read alongside the Song and Ming notices it establishes an unbroken documentary record of the substitution across roughly six centuries.