Arndt–Schulz rule

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Arndt–Schulz rule or Schulz' law is a claimed law concerning the effects of pharmaca or poisons in various concentrations. It states that:[1]

For every substance, small doses stimulate, moderate doses inhibit, large doses kill.

That is to say, highly diluted pharmaca or poisons enhance life processes, while strong concentrations may inhibit these processes and even terminate them.

The rule was named after Hugo Paul Friedrich Schulz and Rudolf Arndt. The latter originally formulated it in 1888. However, the exceptions to the rule are so numerous that it can not be considered a general law. For instance, many paralysing substances have no exciting effect in weak doses, and what constitutes a weak, medium or strong stimulus is highly individual, as pointed out by Arndt himself.

The rule is no longer cited in modern pharmacology texts, having been supplanted by the theory of hormesis.

Scientific Basis for Homeopathy[edit]

This rule has been claimed by some homeopaths as supporting their theories.[1] However, this rule does not apply to the dilutions typically used by homeopaths, which have a high probability of containing no molecules of the diluted substance. To explain the purported therapeutic powers of homeopathic remedies Jacques Benveniste created the postulate of "water memory". However, subsequent research has shown that the perturbations of the hydrogen bond network required for water memory are extremely short, and cannot persist for more that a few femptoseconds. Such evidence renders the water memory hypothesis insufficient to explain any perceived effect of a chemical compound after its removal from a solution.[2]

Historical Perspective[edit]

Early studies of how living systems react to stimuli showed that physiological responses could be obtained with some regularity upon exposure to defined doses. Devising a mechanism for these observations proved difficult, and a significant amount of scientific effort was expended on the subject. The work of Arndt and Schultz, along with that of Ernst Heinrich Weber and Gustav Theodor Fechner, was called upon to provide some explanation for observed relationships between dose and response during the early days of pharmacology. However, other concepts such as Hormesis and Receptor Theory eventually supplanted such "laws" as a more complete and well-defined means of describing how chemicals and physiological systems interact.[3][4]

See also[edit]


  1. ^ a b Paul Callinan. "Homeopathy: How does it work?". Archived from the original on 2008-01-18. Retrieved 15 August 2009. 
  2. ^ Cowan ML, Bruner BD, Huse N, et al. (2005). "Ultrafast memory loss and energy redistribution in the hydrogen bond network of liquid H2O". Nature 434 (7030): 199–202. doi:10.1038/nature03383. PMID 15758995. 
  3. ^ Kenakin, Terry (2009). A Pharmacology Primer. Oxford, UK: Elsevier Academic Press. p. 3. 
  4. ^ Holmstedt, B.; Liljestrand, G. (1981). Readings in Pharmacology. New York, USA: Raven Press.