Physicochemical research focuses on specific characteristics of homeopathic preparations that are measurable using physicochemical techniques. A recent systematic review of more than 200 scientific articles came to the main conclusion that several sets of replicated high-quality experiments provide evidence for specific physicochemical properties of homeopathic preparations. After a selection of articles with sufficient reporting quality, 134 publications were analysed in detail, reporting on 203 experiments. Out of these, 147 (72%) reported specific characteristics of homeopathic preparations. Restricting the data set to high-quality experiments, 23 out of 29 experiments (79%) reported specific properties of homeopathic samples against controls. Contrasting with these interesting empirical observations is, however, that there is yet no consistent interpretation of these physicochemical properties across all experimental approaches. Furthermore, there is no generally accepted theoretical model that puts these empirically observed properties into a context that would form the basis for an explanation of specific effects of homeopathic preparations. However, the existing empirical observations call for further in-depth investigations to identify the mode of action of homeopathic preparations.
Physicochemical research mainly focuses on the question if homeopathic preparations exhibit specific characteristics that are measurable with physicochemical techniques and are distinguishable from those of adequate controls. Furthermore, the relationship between such empirical data and theoretical models needs to be carefully evaluated to finally understand how empirically measured characteristics of homeopathic preparations relate to the underlying physicochemical mode of action .
The field of physicochemical research into homeopathic preparations has recently been systematically reviewed (Review: part one, two, three). This exhaustive survey revealed more than 200 peer-reviewed articles, which were assessed with regard to the quality of publication. Publication quality of 134 articles was judged to be sufficient to further analyse them in detail. These articles were split into 203 individual experiments, defined as series of measurements using uniform experimental methods applied on a homogenous set of samples.
The analysis of these publications and individual experiments revealed various aspects of research in this field. The quality of publications and the number of publications sharply increased after the year 2000, with main contributions coming from Italy, India, Germany and Switzerland. The most frequently used physicochemical methods were measurements of electrical impedance, analytical methods, optical spectroscopy and nuclear magnetic resonance-based methods.
Most investigations were of exploratory nature, researching the presence (or absence) of a quantifiable difference between homeopathic preparations and controls when investigated using a particular technique. More than 70% of all experiments reported differences between homeopathic preparations and controls. However, only about 20% of the experiments used coded (blinded) and randomized samples, and 28% were evaluated with inferential statistics. Furthermore, only 37% used succussed or potentized controls, which is the only reliable way to identify specific properties of homeopathic preparations.
In the above mentioned analysis, a subgroup of high-quality experiments was extracted (using blinding, randomization, inferential statistics, succussed controls and independent production series as quality criteria). In this subgroup, nuclear magnetic resonance and optical spectroscopy were the most frequently used methods. Amongst these experiments, 79% reported differences between homeopathic samples and controls which means that high-quality experiments are more likely to report evidence for specific characteristics of homeopathically potentized samples than experiments of lower quality. In addition, replicated experiments were analysed in detail: for 10 experimental techniques and sample types, 100% of general replicability was observed, with 2–9 replications each. The authors concluded that “several sets of replicated high-quality experiments provide evidence for specific physicochemical properties of homeopathic preparations”.
The search for a theoretical model able to explain these properties – to determine a physicochemical mode of action which would explain the specific effects of highly diluted homeopathic preparations – is still open. Tournier et al. concluded that “there is no consistent evidence to date for a number of proposed working hypotheses, such as stable clathrates, nanoparticles, nano-bubbles, silica compounds, or peptides as being constitutional for the physicochemical homeopathic mode of action”. Three further theoretical approaches – the quantum coherence domain hypothesis, the dynamic water cluster hypothesis, and the weak quantum theory – could currently not be falsified and were recommended for further assessment in specifically designed experimental investigations.
In summary, the majority (79%) of high-quality studies in physicochemical homeopathy research concludes in favour of physically measurable properties of homeopathic preparations over appropriate controls. This highlights the urgent need for more research aimed at understanding the observed phenomena.