THE ATC CLASSIFICATION

The ATC Classification of medicinal substances is in the hands of the WHO Collaborating Centre for Drug Statistics Methodology at the Norwegian Medicinal Depot (NMD) in Oslo.

ATC stands for Anatomical, Therapeutic and Chemical, and the system has 5 levels.

The 1st level consists of 14 main groups, lettered A to V and most often named by the anatomical site of action.
The 2nd and 3rd levels focus therapeutic uses and pharmacological subgroups, and
The 4th and 5th levels focus chemical - group / subgroup specific, generic and brand - names.

All new entries in the ATC classification system are assigned on request from the users. Strictly chemical names and formulas are as a rule not included.

The levels are somewhat heterogenous. The main groups at level 1 do not always equal an anatomical site; e.g. J Infectious diseases. Headings on level 2 may sometimes refer to substances - e.g. J01 antibiotics for systemic use, and level 4 may also carry therapeutic indications. To find a comprehensive view of the use of e.g. corticosteroids, local use is to be found under Skin (D07) and the systemic use under Hormones, excl. sex hormones (H02).

After the generic name of a substance on level 5, ATC enumerates brand names of products, the latter being defined as pharmacological packages which can be dispensed, prescribed and purchased. Products containing one active substance - or several active substances from the same therapeutic group - are considered as plain. Plain products may contain auxiliary substances, aimed to reduce pain, discomfort or adverse effects, or to increase drug stability. Products containing two or more active substances from different therapeutic groups are regarded as combination products.

Example classification:

Level 1	Anatomical	N	Central Nervous system
Level 2	Therapeutic	N05	Neuroleptics
Level 3	Therapeutic subgroup	N05B	Sedatives
Level 4	Chemical	N05BA	Benzodiazepines
Level 5	Chemical subgroup	N05BA01	Diazepam

The main groups at Level 1 = A to V, and some selected subgroups at Level 2 = XXX, are as follows:

A Alimentary tract and Metabolism A01 Stomatological preparations A02 Antacids, Drugs for treatment of peptic ulcer and flatulence A03 Antispasmodic and Anticholinergic agents A04 Antiemetics and Antinauseants A06 Laxatives A07 Antidiarrhoeals; Intestinal antiinflammatory and antiinfective agents A10 Antidiabetic therapy A14 Anabolic steroids	L Tumours and Immune system derangements L01 Cytostatic / Cytotoxic agents L02 Endocrine therapy L03 Immunostimulating agents L04 Immunosuppressive agents
B Blood and Blood forming organs B01 Anticoagulants B02 Haemostatics B03 Antianaemic preparations B06 Other haematological agents	M Musculo-skeletal system M01 Antiinflammatory and Antirheumatic agents M02 Topical products for Joint and Muscular pain M03 Muscle relaxants M04 Antigout agents M05 Agents affecting skeletal disease
C Cardiovascular system C01 Drugs for heart diseases C02 Antihypertensives C03 Diuretics C04 Drugs for peripheral vascular disease C07 Beta receptor blocking agents C08 Calcium channel antagonists C09 Drugs affecting the Renin-Angiotensin system C10 Serum lipid lowering drugs	N Central Nervous system N01 Anaesthetics N02 Analgesics N03 Antieleptics N04 Drugs against Parkinsonism N05 Neuroleptics, Ataractics and Hypnotics N06 Psychoanaleptics - Antidepressives and Psychostimulants
D Skin D01 Antimycotics D02 Protectives and Emollients D04 Antipruritics D05 Antipsoriatics D06 Antibacterials and Antivirals D07 Glucocorticosteroids, for external - topical - use	P Antiparasitic products P01 Antiprotozoals P02 Anthelmintics
G Genitourinary system and sex hormones G01 Gynecological antiinfectives and antiseptics G03 Sex hormones	R Respiratory system R01 Drugs for nasal disease R02 Drugs for pharyngeal and laryngeal disease R03 Antiasthmatics R05 Drugs against cough R06 Antihistamines for systemic use
H Hormones, excl sex hormones H01 Pituitary and Hypothalamic hormones H02 Corticosteroids, for systemic use H03 Thyroid hormones and Antithyroid drugs H04 Pancreatic hormones H05 Drugs affecting Calcium metabolism	S Sensory organs S01 Ophtalmologicals S02 Otologicals
J Infectious diseases J01 Antibacterials, for systemic use J02 Antimycotics, for systemic use, excl griseofulvin J04 Drugs against mycobacterias J05 Antivirals, for systemic use J06 Immune sera and Immunoglobulins J07 Vaccines	V Various V01 Allergens V02 Agents for intoxications, overdoses and abuse V03 Diagnostic aids V04 Nutritional agents V05 Technical aids V06 Contrast media

FURTHER READING
WHO Collaborating Centre for Drug Statistics Methodology
WHO INT - The International Pharmacopeia
WHO - Index of Pharmacopoeias