CCR: Now, moving onto something more controversial. Here is a statement one can find on the Web: “It is widely accepted that marijuana has two different species: Cannabis indica and Cannabis sativa.” This was of course also the opinion of the great 18th century naturalist, Jean-Baptiste Lamarck, but would academic botanists today agree with this statement?
Dr. Russo: Botanical taxonomists never agree on anything for very long! To paraphrase and expropriate an old Yiddish expression: 12 botanical taxonomists, 25 different opinions. Many classical botanists would argue for Cannabis as one polymorphic species based on the ability of all its types to interbreed. However, if this were true, hundreds of neotropical gesneriads (Gesneriaceae, members of the African violet family) would all be one species since they readily hybridize and produce fertile offspring. It is clear that there are many chemotypes of Cannabis: THC predominant, CBD predominant, and mixed types. This is a good basic classification, but it has also been possible to selectively breed for other chemotypes expressing high titers of THCV, cannabidivarin, cannabichromene, and even ones producing 100% of its cannabinoids as cannabigerol, or others with no cannabinoids at all. The debate continues. Some espouse Cannabis as a single species, while others describe up to four: 
Cannabis sativa, 
Cannabis indica, 
Cannabis ruderalis, and 
Cannabis afghanica (or 
kafiristanica).
6,
7
CCR: Some users describe the psychoactive effects of Cannabis indica and sativa as being distinctive, even opposite. But are they really? Beyond self-reports from users, is there any hard evidence for pharmacologically different species of Cannabis?
Dr. Russo: There are biochemically distinct strains of Cannabis, but the 
sativa/
indica distinction as commonly applied in the lay literature is total nonsense and an exercise in futility. One cannot in any way currently guess the biochemical content of a given Cannabis plant based on its height, branching, or leaf morphology. The degree of interbreeding/hybridization is such that only a biochemical assay tells a potential consumer or scientist what is really in the plant. It is essential that future commerce allows complete and accurate cannabinoid and terpenoid profiles to be available.
CCR: Sativa is often described as being uplifting and energetic, whereas indica as being relaxing and calming. Can you speculate on what could be the basis for these perceived differences?
Dr. Russo: We would all prefer simple nostrums to explain complex systems, but this is futile and even potentially dangerous in the context of a psychoactive drug such as Cannabis. Once again, it is necessary to quantify the biochemical components of a given Cannabis strain and correlate these with the observed effects in real patients. Beyond the increasing number of CBD predominant strains in recent years, almost all Cannabis on the market has been from high-THC strains. The differences in observed effects in Cannabis are then due to their terpenoid content, which is rarely assayed, let alone reported to potential consumers. The sedation of the so-called 
indica strains is falsely attributed to CBD content when, in fact, CBD is stimulating in low and moderate doses! Rather, sedation in most common Cannabis strains is attributable to their myrcene content, a monoterpene with a strongly sedative couch-lock effect that resembles a narcotic. In contrast, a high limonene content (common to citrus peels) will be uplifting on mood, while the presence of the relatively rare terpene in Cannabis, alpha-pinene, can effectively reduce or eliminate the short-term memory impairment classically induced by THC.
2,
8
CCR: How do you think one could address the sativa/indica dichotomy in a scientifically sound manner?
Dr. Russo: Since the taxonomists cannot agree, I would strongly encourage the scientific community, the press, and the public to abandon the 
sativa/
indica nomenclature and rather insist that accurate biochemical assays on cannabinoid and terpenoid profiles be available for Cannabis in both the medical and recreational markets. Scientific accuracy and the public health demand no less than this.