PDR for one.
Any medical text used to define drugs (the kind of books used in nursing schools and medical schools, not the kind found in head shops).
For instance:
The term “psychedelic” is used interchangeably with “psychotomimetic” and “hallucinogen”, thus it can refer to a large number of drugs such as classical hallucinogens (LSD, psilocybin, mescaline, etc.), empathogen-entactogens (e.g. MDMA), cannabinoids, and some dissociative drugs.
There are hundreds of other sources, but you can believe what you want. I have learned what I know directly from licensed professionals that work daily with such drugs.
Interesting! Ties in with this: "Hallucinogens are a diverse group of drugs that cause an alteration in perception, thought, or mood. A rather heterogeneous group, these compounds have different chemical structures, different mechanisms of action, and different adverse effects. Despite their name, most hallucinogens do not consistently cause hallucinations, which are defined as false sensations that have no basis in reality. Often, they are more likely to cause changes in mood or in thought than actual hallucinations." (emphasis added) - http://emedicine.medscape.com/article/293752-overview