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Hydromethylthionine
Hydromethylthionine (leucomethylene blue, LMTM, TRx0237) is the reduced form of methylene blue, an oral tau aggregation inhibitor developed by TauRx for Alzheimer's disease and frontotemporal dementia; investigational, MHRA review expected 2026.
Hydromorphone
Hydromorphone (Dilaudid), a semisynthetic Schedule II opioid agonist derived from morphine, two to eight times morphine's potency, no active metabolites, used for moderate to severe postoperative and cancer pain.
Hydronephrosis
Hydronephrosis is swelling of the kidney from urine build-up, dilating the renal pelvis and calices. Causes include stones, pregnancy, and prostate enlargement; it does not always mean obstruction, and treatment ranges from drainage to surgery.
Hydronephrosis with ureteropelvic junction obstruction
Hydronephrosis with ureteropelvic junction obstruction (ICD-11 GB56.0): urine outflow blocked where the renal pelvis joins the ureter, dilating the kidney. Incidence 1:1,500, male predominance, treated by pyeloplasty with about 95% success.
Hydrophilic Contact Lenses
Hydrophilic (soft) contact lenses: water-containing HEMA or silicone hydrogel polymer lenses worn on the eye; FDA Class II under 21 CFR 886.5925; hydrogels date to Wichterle's 1961 spin-cast patent, silicone hydrogels to 1999.
Hydrops fetalis
Hydrops fetalis, including non-immune hydrops fetalis (NIHF), is abnormal fluid accumulation in two or more fetal compartments. Causes include aneuploidy, RASopathies, cardiac anomalies, and infection; survival often under 50%.
Hydrops of gallbladder
Hydrops of gallbladder (gallbladder mucocele, hydropic gallbladder), ICD-11 DC10.1: cystic duct obstruction, usually by an impacted gallstone, replacing bile with clear mucus-like "white bile"; treated by laparoscopic cholecystectomy.
Hydrosalpinx
Hydrosalpinx is a fallopian tube blocked at its far end and swollen with fluid, most often after pelvic inflammatory disease, and a known cause of infertility.
Hydrostatic shock
Hydrostatic shock, also called hydraulic shock, is the contested hypothesis that a bullet's ballistic pressure wave injures tissue remote from the wound track; critics attribute remote damage to temporary cavitation instead.
Hydrotherapy
Hydrotherapy (aquatic physiotherapy, balneotherapy): therapeutic external use of water, from cold immersion (11–15 °C) and warm baths (38–40 °C) to pool exercise. Small trial benefits for osteoarthritis and fibromyalgia pain; not FDA-regulated; no cure claims proven.
Hydroureter
Hydroureter is the abnormal enlargement of the ureter, the tube carrying urine from kidney to bladder, most often caused by a blockage; it occurs at all ages.
Hydroxocobalamin
Hydroxocobalamin (Cyanokit, Cobalin-H, Neo-Cytamen) is a manufactured vitamin B12 (cobalamin) form given by injection for B12 deficiency and, at 5 g IV, as a cyanide-poisoning antidote; preferred in the UK over cyanocobalamin for longer retention.
Hydroxyamphetamine
Hydroxyamphetamine (4-hydroxyamphetamine, Paredrine, Paremyd with tropicamide) is an indirect sympathomimetic amine that releases norepinephrine to dilate the pupil and localize Horner's syndrome lesions; now largely superseded by apraclonidine.
Hydroxycamptothecin
Hydroxycamptothecin (10-hydroxycamptothecin, HCPT, 10-羟基喜树碱), a topoisomerase I-inhibiting alkaloid from Camptotheca acuminata, about 30 times more active than camptothecin but limited by lactone instability and poor water solubility.
Hydroxycarbamide
Hydroxycarbamide (hydroxyurea), a ribonucleotide reductase inhibitor synthesized in 1869, FDA-approved 1967 as an antineoplastic and 1998 for sickle cell anemia; raises HbF, reduces pain crises, mainstay disease-modifying SCD drug.
Hydroxychloroquine
Hydroxychloroquine (Plaquenil, HCQ), a 4-aminoquinoline DMARD derived from chloroquine and quinine, treats rheumatoid arthritis, lupus, skin conditions, and malaria; large trials found no COVID-19 benefit, and retinopathy is the main long-term risk.
Hydroxycut
Hydroxycut, also sold as Hydroxycut Advanced and Hydroxycut Hardcore, is an Iovate/MuscleTech weight loss supplement brand recalled in 2009 after 23 FDA-reported liver injury cases and one death, with reformulated products still on sale.
Hydroxykynureninuria
Hydroxykynureninuria, also known as xanthurenic aciduria or kynureninase deficiency, is a very rare inherited disorder of tryptophan metabolism with large urinary losses of xanthurenic acid, kynurenine, and 3-hydroxykynurenine.
Hydroxyprogesterone caproate
Hydroxyprogesterone caproate (17-OHPC; Delalutin, Makena, Proluton Depot) is a synthetic long-acting progestin ester given weekly by intramuscular injection. FDA approved it in 2011 to prevent recurrent preterm birth and withdrew that approval in April 2023; the EU suspended it in 2024.
Hydroxystilbamidine
Hydroxystilbamidine (2-hydroxy-4,4'-stilbenedicarboxamidine, CAS 495-99-8) is a stilbenoid aromatic diamidine. Its isethionate salt, approved in 1953 and now discontinued, treated blastomycosis and leishmaniasis; the dye remains a histochemical stain and neuroanatomic tracer.
Hydroxyurea therapy
Hydroxyurea (hydroxycarbamide) therapy is oral drug treatment that inhibits ribonucleotide reductase and raises fetal hemoglobin, the mainstay disease-modifying drug for sickle cell disease since FDA approval in 1998.
Hydroxyzine
Hydroxyzine (Atarax, Vistaril) is a first-generation sedating antihistamine used for itching, anxiety, and surgical sedation, in use since 1955, with a small but definite QT-prolongation risk that led to 2015 EMA dose restrictions.
HyFerr study
HyFerr (Candidate Gene for Hyperferritinemia, NCT05659017) is an observational genetic study at the University of Milano Bicocca and San Gerardo Hospital, Monza, sequencing a candidate gene in 100 patients with unexplained hyperferritinemia without iron overload; it yielded biallelic STAB1 variants as a novel cause.
Hygiene
Hygiene: conditions and practices maintaining health and preventing disease spread, covering hand hygiene, environmental cleaning, and WASH. Key facts: WHO-5 hospital strategy, 80% global basic hygiene coverage in 2024, 394,000 diarrhoea deaths from unsafe hand hygiene.
Hygiene hypothesis
Hygiene hypothesis: Strachan's 1989 proposal that reduced early-life microbial exposure impairs immune maturation, raising allergy and autoimmune risk; revised as the old friends and biodiversity hypotheses.
Hymen
Hymen: thin tissue at the vaginal opening, also called the maidenhead, with no known function. Its appearance cannot indicate sexual history; WHO and UN agencies condemn hymen-based virginity testing as unscientific and harmful.
Hyoid bone
Hyoid bone: free-floating U-shaped neck bone of body, greater horns, and lesser horns, anchoring tongue and swallowing muscles; fractures of the greater horns indicate neck violence, and shape varies widely between individuals.
Hyoscine butylbromide
Hyoscine butylbromide, also called butylscopolamine and best known as Buscopan, is an antispasmodic drug used since 1951 to relieve abdominal cramps, irritable bowel syndrome, and spasms of the urinary tract.
Hyoscyamine
Hyoscyamine, a tropane alkaloid from Atropa belladonna and the L-isomer of atropine, is an antimuscarinic antispasmodic used for GI spasm and IBS, with weak efficacy evidence and anticholinergic side effects.
Hyper-empathy
Hyper-empathy (hyperempathy) is above-average, overwhelming empathy, not a DSM-5 diagnosis; described mainly by autistic people and framed by Smith's empathy imbalance hypothesis of high affective with low cognitive empathy.