Cannabis preparations have been used by man for over 5000 years. Early use was associated with medical applications. However, as newer and better medicinal agents were discovered, the use of crude drugs from Cannabis lost favor in clinics throughout the world. This trend continued, and today there are no crude Cannabis drugs used in modern medical clinics. The same Cannabis preparations once accepted as therapeutically useful drugs have gained acceptance as innocuous drugs of leisure in most countries of the world. The rapid and broad increase in the use and abuse of these drugs resulted in Cannabis being controlled by international treaties. Local, national, and international agencies are charged with the responsibility of enforcing these treaties. Crude Cannabis preparations once of medical use are now illegal. Thus, marihuana, hashish, dagga, bhang, ganja, hash oil, sinsemilla, etc., comprise the world's most common and widely used group of illicit drugs. Worldwide, approximately 300 million people use one or more of these crude drugs. It is estimated that in the United States of America 36 million people have used some form of Cannabis. Current scientific opinions about Cannabis are not always based on rational and reproducible scientific facts, but on emotion. Although the Cannabis and health issue is of interest to all health-related scientific disciplines and agencies of the world, due to the emotional issue, it is possible that scientific experiments may never clarify the pharmacology of Cannabis. The general opinion held by much of the broadly diversified scientific community is that Cannabis preparations can be evaluated solely on (-)-Δ⁹-trans-tetrahydrocannabinol (Δ⁹-THC) content, thereby neglecting other cannabinoids and chemicals in the crude drug. It is easy to understand how this concept came to be accepted, since Δ⁹-THC is always referenced as the 'active compound' in Cannabis, and data from 'synthetic marihuana' (Δ⁹-THC) is taken as being synonymous with data from marihuana. This has fostered the impression that marihuana and other crude drugs from Cannabis are singular in composition and uniform in potency with hashish being 'X' times as strong as marihuana, etc. Therefore, it is critical to the scientific community that a document fully elucidating the current state of the knowledge of naturally occurring constituents in Cannabis be published. Although over 1000 scientific papers have been published on Cannabis and its constituents and many reviews have been written on Cannabis constituents and cannabinoid chemistry, all are of limited value in the natural profile of Cannabis and are of even less value for elucidating chemically why confusion exists and may continue to exist in the biological evaluation of the crude drugs obtained from Cannabis. The present review is structured around all known natural constituents of Cannabis sativa L. Emphasis will be placed on those compounds actually isolated. Some constituents considered will be discussed; and commonly occurring plant constituents never to be artifacts within the plant, such as those shown to be present by spectral data, will be considered. Synthetic chemistry, nor chemistry of the pyrolysis process which occurs when Cannabis preparations are smoked, will be considered. These subjects have been adequately covered by Razdan and others and by a United Nations Narcotics Laboratory document, respectively. However, the paper will include a brief review of the botany and chemical classification systems used for Cannabis with emphasis on the chemical aspects rather than the botanical aspects.