Grapefruit seed extract

Tier 3 — weak evidence · CYP3A4 modulator · Citrus polyphenol · Caution

Naringin/naringenin-rich citrus extract that is a strong CYP3A4 and P-glycoprotein inhibitor — useful AS A CAUTION FLAG, not as a recommended supplement. Co-administration with statins, calcium-channel blockers, immunosuppressants, antiarrhythmics, PDE-5 inhibitors, and many psychiatric drugs can dangerously raise drug levels. Most commercial 'GSE' products are actually contaminated with synthetic preservatives (benzethonium chloride, methylparaben). The extract itself has no compelling indication; we list it primarily so the medication-interaction logic can flag it.

Dose: Avoid in patients on CYP3A4-substrate medications