Complex sentence: Many drug preparations used in anthroposophic medicine are ultra-diluted substances, similar to those used in homeopathy, and these are completely harmless, except when used as a substitute for mainstream medicine, thereby missing an effective cure.
Split into simpler sentences: Many drug preparations used in anthroposophic medicine are ultra-diluted substances, similar to those used in homeopathy. Homeopathic dilutions themselves are completely harmless, except when used as a substitute for mainstream medicine, thereby missing an effective cure.