- Irregular sleep-wake rhythm disorder
- Irreversible antagonist
- Irreversible electroporation
- Irritability
- Irritable bowel syndrome
- Irritant contact dermatitis
- Irritants
- Irvine-Gass syndrome
- Irvingia gabonensis
- Isatin
- Isatis tinctoria
- Ischemia
- Ischemic cardiomyopathy
- Ischemic cascade
- Ischemic colitis
- Ischemic compression
- Ischemic heart disease
- Ischemic hepatitis
- Ischemic injury
- Ischemic monomelic neuropathy
- Ischemic optic neuropathy
- Ischemic preconditioning
- Ischemic stroke
- Ischial
- Ischial spine
- Ischial tuberosity
- Ischioanal fossa
- Ischiocavernosus
- Ischiocavernosus muscle
- Ischiofemoral
- Ischiofemoral ligament
- Ischiopagi
- Isethionate
- Islet cell transplantation
- Islets of Langerhans
- Isoalloxazine
- Isoantibodies
- Isoaspartate
- Isobaric tag for relative and absolute quantitation
- Isoborneol
- Isobutanol
- Isobutene
- Isobutyl alcohol
- Isobutyl cyanoacrylate
- Isocarboxazid
- Isocenter
- Isochromosome
- Isocitrate dehydrogenase
- Isocitric acid
- Isocoumarin
- Isocyanate group
- Isocyanates
- Isocyanide
- Isodesmosine
- Isoelectric focusing
- Isoelectric point
- Isoenzymes
- Isoetarine
- Isoferulic acid
- Isoflavones
- Isoflurane
- Isograft
- Isohumulone
- Isoinertial
- Isolated hepatic perfusion
- Isolated hypogonadotropic hypogonadism
- Isolation
- Isolation by distance
- Isolation chip
- Isolation ward
- Isoleucine
- Isoliquiritigenin
- Isomalt
- Isomaltase
- Isomaltose
- Isomer
- Isomerization
- Isometheptene
- Isometric exercise
- Isoniazid
- Isonicotinic acid
- Isopentenyl pyrophosphate
- Isopeptidase
- Isopeptide bonds
- Isophane insulin
- Isophorone
- Isophthalic acid
- Isopimaric acid
- Isopimpinellin
- Isoprenaline
- Isoprene
- Isoprenoids
- Isopropamide
- Isopropyl alcohol
- Isopropyl myristate
- Isopropyl β-D-1-thiogalactopyranoside
- Isoprostane
- Isoquinoline alkaloids
- Isorhamnetin
- Isosakuranetin
- Isoschizomer
- Isosorbide
- Isosorbide dinitrate
- Isosorbide mononitrate
- Isospora
- Isosporiasis
- Isostere
- Isostructural
- Isosulfan blue
- Isosurface
- Isotachophoresis
- Isothermal titration calorimetry
- Isothiazolinones
- Isothiocyanate
- Isothipendyl
- Isotonic
- Isotonic solution
- Isotope dilution
- Isotope-coded affinity tags
- Isotopes of iodine
- Isotopes of potassium
- Isotopic labeling
- Isotopomers
- Isotretinoin
- Isotypes
- Isovaleraldehyde
- Isovaleric acidemia
- Isovaleryl-CoA dehydrogenase
- Isovanillin
- Isovolumetric contraction
- Isovolumic relaxation time
- Isoxazole
- Isozymes
- Isradipine
- Istaroxime
- Istradefylline
- Itai-itai disease
- Ital
- Itching
- Item analysis
- Item bank
- Item response theory
- Iterative reconstruction
- Itraconazole
- Ivabradine
- Ivacaftor
- Ivemark syndrome
- Ivermectin
- Ivosidenib
- Ixabepilone