For many years the ACD has had a page attempting a rundown of the genetics of cannabis and chemistry of the active substances.
Over the years the science of cannabis has moved on. For many of those years the ACD has also had a forum where real experts report on the latest developments. This renders most of what was written here obsolete.
Nevertheless, here is a very short summary:
Psychoactive Chemicals
Concentrated in the resinous trichomes smothering cannabis buds are a group of substances known collectively as cannabinoids. Over 100 different cannabinoids have been isolated so far. Research is continuing to reveal more psychoactive and medicinal properties of the various cannabinoids but two important ones are THC and CBD.
THC (D9 THC or delta-9-trans-tetrahydrocannabinol and D8 THC) is the most important psychoactive cannabinoid.
CBD (cannabidiol) is one of cannabinoids thought to have medicinal benefits. It is also thought to moderate the effects of THC.
We used to think that THC was what it's all about and that CBD had a negative effect. It's now becoming clear that it's much more complicated than that and that all of the cannabinoids work together to produce a fully rounded cannabis experience.
Like the chemistry, modern thinking on cannabis genetics suggests that it might also be more complicated than first thought. There is much debate about how many species or subspecies of cannabis there are and whether the divisions are natural or the result of human intervention.
The traditional view goes something like this:
Cannabis Sativa is the tallest, most straggly species with fine leaflets. It originates in warm lowland regions. Sativa produces a sweet mild smoke and is associated with getting 'high'.
Cannabis Indica is a more compact, conical, plant with broader leaflets. It originates in slightly cooler, highland locations. Indicas produce a thick, pungent smoke associated with getting 'stoned'.
Cannabis Ruderalis is a small weedy plant of little significance.
Sativa tends to have a higher THC to CBD ratio. Indica tends to be more resinous and mature faster.
Cross-breeding plants from around the world has created countless hybrids. These can be faster growing and more resinous than pure Sativas and yet have a better THC to CBD ratio than pure Indicas.
Skunk
Here in the UK all modern home-grown grass tends to be given the generic name of "Skunk".
The classic Skunk, perhaps the most famous genetic line, was originally bred in the USA from a combination of Latin American Sativas and Afghani Indica. The original Skunk Number 1 was 75% Sativa and 25% Indica.
Most menus have some indication of whether products are predominantly Indica or Sativa.
Names including words like Kush, Cheese, White Widow and Northern Lights are likely to be towards the Indica end of the spectrum. Terms such as Haze, Amnesia, Jack Herer and Thai suggest more Sativa.
Personally, when in Amsterdam, I like to smoke strains from the more sativa end of the scale during the day and move towards the indicas in the evening. That's because I find the heavier indicas quite soporific and sativas more uplifting and less de-motivating. If you're looking for relaxation or are prone to paranoia when stoned, however, you may wish to stick to the indicas.