This paper discusses the nature of the active ingredient of homeopathic ultramolecular dilutions in terms of quantitative physics.First, the problem of the nature of an active ingredient in ultramolecular dilutions is analysed leading to the recognition of the necessity of characterizing the active ingredient as a non-local quality.Second, non-locality in quantum mechanics, which is used as a paradigm, is formally presented.Third, a generalization of quantum mechanics is considered, focussing on the consequences of weakening of the axioms.The formal treatment leads to the possible extension of the validity of quantum theory to macroscopic or even non-physical systems under certain circumstances with a while maintaining non-local behaviour. With respect to the survival of entanglement in such non-quantum systems a strong relationship between homeopathy and non-local behaviour can be envisaged. I describe how several authors apply this relationship. In conclusion, the paper reviews how quantum mechanics is closely related to information theory but why weak quantum theory and homeopathy have not hitherto been related in the same way.