Classical homeopathy is generally defined as a system of medical treatment based on the use of minute quantities of remedies that in larger doses produce effects similar to those of the disease being treated. It is believed that very small doses of a medication could have very powerful healing effects because their potency could be affected by vigorous and methodical shaking. This is referred to this alleged increase in potency by vigorous shaking as dynamization. It is also thought succussion could release immaterial and spiritual powers, thereby making substances more active. Tapping on a leather pad or the heel of the hand was alleged to double the dilution. Examples include: the use of an isopathic (disease associated) agent as a first prescription in a stuck case, when the beginning of disease coincides with a specific event such as vaccination; the use of a chemically related substance when a remedy fails yet seems well-indicated; and more recently, the use of substances based on their natural classification (the periodic table or biological taxonomy). This last approach is considered to be promising by some in the homeopathic community, because it allows for grouping remedies and classifying the ever-burgeoning Materia Medica, but is rejected by many purists because it involves speculation about remedy action without proper provings. There are estimated to be more than 100,000 physicians practicing homeopathy worldwide, with an estimated 500 million people receiving treatment. More than 12,000 medical doctors and licensed health care practitioners administer homeopathic treatment in the UK, France, and Germany. Since 2001, homeopathy is regulated in the European Union by Directive 2001/83/EC; the latest amendments make it compulsory for member states to implement a simple registration procedure for homeopathic remedies. In the UK, homeopathic remedies may be sold over the counter. The UK has five homeopathic hospitals where treatment, funded by the National Health Service, is available and many regional clinics. Homeopathy is not practiced by most of the medical profession, but there is a core of public support, including from the Prince of Wales.