Chemical substance made in a laboratory. Other chemical substances commonly encountered in pure form are diamond (carbon), gold, table salt (sodium chloride) and refined sugar (sucrose). However, in practice, no substance is entirely pure, and chemical purity is specified according to the intended use of the chemical. Chemical substances exist as solids, liquids, gases, or plasma, and may change between these phases of matter with changes in temperature or pressure. Chemical substances may be combined or converted to others by means of chemical reactions. Forms of energy, such as light and heat, are not matter, and are thus not "substances" in this
Compound analgesic Compound analgesic Compound analgesics are those with multiple active ingredients; they include many of the stronger prescription analgesics. Active ingredients that have been commonly used in compound analgesics include: Several such formulations have disappeared from over-the-counter status in drug store aisles and other retail outlets. One example is APC (aspirin, phenacetin, and caffeine) compound tablets common from the 1940s to 1983; because of harmful side effects of phenacetin, Anacin in the U.S. was reformulated to eliminate it; while Vincent's APC is no longer sold. Some others have been judged to contribute too often to substance abuse. Another example is Bex,