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Hallucination
Hallucination: a sensory perception without an external stimulus, in any modality. Also called voice hearing (auditory). Occurs in ~9.6% of the general population lifetime, 80% in schizophrenia; not pathognomonic of any disorder.
Hallucinogen
Hallucinogens are drugs that profoundly alter perception, mood, and thought, including classic psychedelics (LSD, psilocybin, DMT), dissociatives (ketamine, PCP), MDMA, and atypical agents like ibogaine, with history, effects, risks, and regulation.
Hallucinogen dependence
Hallucinogen dependence is a disorder of dysregulated hallucinogen use, marked by impaired control, use taking precedence over other pursuits, and persistence despite harm; ICD-11 classifies it under code 6C49.2.
Hallucinogen intoxication
Hallucinogen intoxication (ICD-11 6C49.3) is a transient condition during or shortly after hallucinogen use, with perceptual, cognitive, and autonomic disturbances; managed mainly with reassurance and benzodiazepines, with hyperthermia and tachydysrhythmias as key dangers.
Hallucinogen persisting perception disorder
Hallucinogen persisting perception disorder (HPPD), formerly post-hallucinogen perception disorder or flashback syndrome, is a DSM-5 disorder (292.89, F16.983) of persistent re-experienced perceptual disturbances after hallucinogen use, with intact reality testing, roughly 4% estimated prevalence, and antipsychotics worsening symptoms.
Hallucinogen-induced anxiety disorder
Hallucinogen-induced anxiety disorder (ICD-11 6C49.61) is a substance-induced anxiety disorder with symptoms during or soon after hallucinogen intoxication, exceeding intoxication-level anxiety and not better explained by a primary disorder.
Hallucinogen-induced mood disorder
Hallucinogen-induced mood disorder (ICD-11 6C49.60) is mood disturbance, depressive, manic, or mixed, arising during or soon after hallucinogen intoxication, distinguished from primary mood disorders by resolution after cessation of use.
Hallucinogen-induced psychotic disorder
Hallucinogen-induced psychotic disorder (ICD-11 6C49.5): psychotic symptoms such as delusions and hallucinations arising during or soon after hallucinogen intoxication, with 26% pooled transition to schizophrenia.
Hallucinogenic snuff
Hallucinogenic snuff (yopo, cohoba, paricá) is a powdered tryptamine preparation inhaled nasally, made from Anadenanthera peregrina seeds rich in bufotenine; used ritually in South America and the pre-Columbian Caribbean for millennia.
Hallux rigidus
Hallux rigidus is osteoarthritis of the joint at the base of the great toe, causing pain, stiffness, and limited upward bending; it mainly develops after age 40.
Hallux valgus surgery
Hallux valgus surgery is a set of orthopedic procedures that realign a deviated big toe, or bunion, by cutting and repositioning bone, balancing soft tissue, or fusing a joint.
Halobetasol propionate
Halobetasol propionate: ultra-high potency (class I) synthetic topical corticosteroid (Ultravate, Bryhali, Lexette, Duobrii combination) for plaque psoriasis; 0.05% and 0.01% formulations, two-week to eight-week use limits, 50 g/week cap.
Haloperidol
Haloperidol (Haldol), a butyrophenone typical antipsychotic synthesized at Janssen in Belgium on 11 February 1958 as R-1625, acts via dopamine D2 blockade; WHO essential medicine since 1977 for psychosis, with EPS and QT risks.
Haloprogin
Haloprogin (C9H4Cl3IO, brand Halotex) is a discontinued halogenated phenolic ether topical antifungal, approved 1982, used at 1% twice daily for tinea and cutaneous candidiasis; mechanism unknown, more skin irritation than clotrimazole.
Halothane
Halothane (Fluothane), a halogenated hydrocarbon inhalational anesthetic introduced in 1956, C2HBrClF3; removed from the WHO Essential Medicines List in 2025 over hepatotoxicity and greenhouse gas impact, still used in some low-resource settings.
HALT-C trial
HALT-C (Hepatitis C Antiviral Long-term Treatment against Cirrhosis) trial, a US NIH randomized trial testing low-dose maintenance peginterferon in prior interferon nonresponders with advanced hepatitis C fibrosis.
Ham test
The Ham test, also called the acidified serum lysis test, is a hematology assay for paroxysmal nocturnal hemoglobinuria, developed by Thomas Hale Ham in 1939.
Hamartoma
A hamartoma is a non-cancerous lesion made of an unusual mixture of cells and tissues normally found at the site where it forms, often discovered incidentally on imaging.
Hamilton Rating Scale for Depression
Hamilton Rating Scale for Depression (HAM-D, HRSD, HDRS): clinician-administered 21-item depression severity scale by Max Hamilton, 1960, scored on first 17 items; gold standard in trials, remission cutoff ≤7.
Hammer toe
Hammer toe (hammertoe): flexion deformity of a lesser toe at the PIP joint, up to 20% of foot and ankle issues; treated first with footwear and orthotics, surgery for rigid cases.
Hamstring
Hamstrings: biceps femoris, semitendinosus, and semimembranosus, the posterior thigh muscles that flex the knee and extend the hip. Commonly strained during sprinting late swing; Nordic hamstring exercise cuts injury rates about 51%.
Hamycin
Hamycin, a heptaene polyene antifungal antibiotic from Streptomyces pimprina, marketed in India from 1963 for Candida infections; ergosterol-binding, toxic, later liposomized, now discontinued.
Hand
Hand: terminal organ of the human upper limb with 27 bones (8 carpals, 5 metacarpals, 14 phalanges), an opposable thumb via the saddle trapeziometacarpal joint, power and precision grips, and dense tactile innervation.
Hand Function Test
The Hand Function Test, known as the Jebsen-Taylor Hand Function Test, times seven simulated daily tasks per hand to measure hand function in stroke, arthritis, and hand injury.
Hand sanitizer
Hand sanitizer (alcohol-based hand rub, ABHR) is a liquid, gel, or foam applied to hands to kill germs; CDC recommends at least 60% alcohol, formulation matters more than alcohol concentration, and it cannot remove C. difficile spores or chemicals.
Hand Strength
Hand strength (grip strength, handgrip strength) is the force exerted when gripping or grasping, measured with a dynamometer. Used to diagnose sarcopenia and frailty and to predict mortality; reliability ICC about 0.92 to 0.96.
Hand surgery & rehabilitation
Hand surgery & rehabilitation (Hand Surg Rehabil), ISSN 2468-1229 print, 2468-1210 online, is a bimonthly Elsevier Masson journal from France, official organ of the French, Swiss, and Belgian hand surgery societies, renamed from Chirurgie de la main in 2016 and indexed in MEDLINE.
Hand transplantation
Hand transplantation: vascularized composite allotransplantation of a donor hand to an amputee. First attempted Ecuador 1964; first success Lyon 1998 (Dubernard); requires lifelong immunosuppression; distinct from replantation and prosthetics.
Hand washing
Hand washing: cleaning hands with soap and water (hand hygiene, alongside alcohol-based hand rubs) to remove germs. CDC technique: 20 seconds scrubbing; reduces diarrhea 23-40%, respiratory illness 16-21%; only 19% globally wash with soap after toilet.
Hand-Assisted Laparoscopy
Hand-assisted laparoscopy (HALS), also called hand-assisted laparoscopic surgery, is a hybrid of open and laparoscopic surgery in which the surgeon's gloved hand is inserted through a hand-port device while pneumoperitoneum is maintained, restoring tactile feedback; used in colectomy, splenectomy, and nephrectomy.