Member states are required to ensure that homeopathic products (for oral or external use) can be registered without proof of therapeutic efficacy, provided that there is a sufficient degree of dilution to guarantee the safety of the product; in particular, the product may not contain either more than one part per 10,000 of the mother tincture or more than 1/100th of the smallest dose used in mainstream medicine, with regard to active principles whose presence in a medicinal product results in the obligation to submit a doctor's prescription. In other words, the dilution must be at least D4/4X/C2, and even higher in special cases. Other homeopathic products can still be registered under the normal rules, and products such as Arnica D1 are legally available.