The category of sources below are called "reference sources" (encyclopedias, handbooks, domain-specific dictionaries and more). They provide background information about a significant event, concept or theory. These are a great place to start your research, because the entries/articles in reference works tend to:
Many in the list below are comprehensive enough to incorporate and cite in your assignment as one of the scholarly sources for your "Essay on a Psychoactive Substance" (when in doubt, please check with the Professor).