11. Varieties of

Potency

In addition to various forms of THC, of which delta-9 alone is thought to be psychoactive, cannabis contains some fifty additional chemicals known as cannabinoids. Most of these have not been studied to any significant degree and are present in the plant in only in small quantities. So far, none has been found elsewhere in nature.
    Scientists are still uncertain as to how, if at all, these chemicals contribute to the total effect of marijuana. But experienced smokers are convinced that the particular combination of cannabinoids in a given sample influences its effects, since there are definite variations among individual samples of marijuana that cannot be accounted for by THC levels alone. Some smokers believe that marijuana containing relatively few cannabinoids other than THC produces a very intense high; if this is true, then at least some of the cannabinoids may act as moderating agents.
    The cannabinoid that appears to be most closely related to THC is known as tetrahydrocannabivaren (THCV); it has been found in certain varieties of cannabis from Asia and Africa. THCV seems to work more quickly than THC, bringing on an almost immediate high that subsides within a few minutes. It is not yet known exactly how THCV functions, only that it is most often found in very potent plants.
    A more common chemical is cannabidiol (CBD). It occurs in most varieties; in very low-potency marijuana, CBD can account for up to 95 percent of the cannabinoids in a given sample. Although not psychoactive, CBD does have sedative, analgesic, and antibiotic qualities. It can also be changed into THC—both naturally and artificially—through a device called an isomerizer.[2] CBD actually interferes with the marijuana high, acting as a "downer" with depressant properties; marijuana connoisseurs consider a low CBD content as important as a high THC level. Users report that marijuana with a high concentration of CBD usually produces "knock-out" or "sleepy" effects. While CBD may delay the onset of the high, it can also make it last longer. Generally speaking, good marijuana has a relatively low CBD content, whereas the not-so-good "wild" marijuana in the United States, descended from plants grown for their fiber, may contain a good deal of CBD.
    The other important chemical in cannabis is cannabinol (CBN), which is the immediate degradation product of THC. It is not produced directly by the plant but rather by THC exposed to air. As a result, relatively little CBN is found in fresh samples of marijuana, which are usually more powerful than older material. CBN is thought to heighten the disorienting qualities of THC, making the user feel drugged or dizzy, but not necessarily high. According to one connoisseur, a high on marijuana with a large amount of CBN feels as if it never quite reaches its peak.
    The cannabis plant also produces a biosynthetic precursor to THC, known as THC acid. Over time, the gentle heat of the atmosphere "decarboxylates" the THC acid to active THC.[3] In any plant, therefore, THC exists simultaneously in one of three states: inactive, active, and oxidized into CBN. As Laurence McKinney explains:

Marijuana is always on its way from useless to useless. Too fresh —too much THC acid. Too old—too much CBN. For a smoker to have a good idea of what he's smoking, he would have to know the exact chemical makeup of the sample. He would also have to know how old it was, and how it had been preserved. He can't tell that by looking, smelling or tasting. The only way a smoker can determine the potency of a given sample would be to actually use it.
    Unless you happen to have a gas chromatograph machine in your living room, there's no way that anyone can tell the marijuana's potency or other characteristics without actually using it, no matter where it came from, or when, or how.

    THC is by far the most important ingredient in cannabis, although, as we have seen, it is a tricky and unstable substance. Raphael Mechoulam, the Israeli chemist who first synthesized THC, once examined a piece of hashish whose THC content was only 2 percent on the outside—and a formidable 8 percent on the inside, where it had not been exposed to air. Because of oxidation, marijuana left uncovered for a month will lose most of its potency. Similarly, marijuana that is crushed or strained will also have a lower THC level. "Cleaning your dope right after you buy it," notes David, "is like leaving a bottle of wine in the refrigerator without its cork." Heat, light, and especially air are the enemies of THC, and sophisticated users try to minimize marijuana's contact with all three elements, of Len by keeping their material well wrapped in the refrigerator or even the freezer.
    Now that THC can be manufactured artificially, it is commonly used in place of marijuana in medical studies. It is misleading, however, to assume that the two are interchangeable, because marijuana is clearly more than THC alone. From time to time, pure THC is reportedly sold on the streets, but researchers who have investigated such claims have invariably found that the substance in question is not THC at all but something else—most often PCP ("angel dust"). In fact, it is almost totally unavailable, as the following story illustrates. The head of a major research project at a prestigious urban hospital was eager to sample one of the government-supplied THC pills being administered to patients undergoing cancer chemotherapy (THC is believed to reduce the therapy's bad side effects, especially nausea). But he found security surrounding the project so tight that he was unable to obtain a single capsule for his own use without detection. (Real THC is a clear resin, or sometimes a buff-colored glue; it has also been produced as a soluble white powder.)[4]
    Until around 1975, most marijuana consumed in the United States had an average THC content of slightly more than 1 percent. As little as.5 percent THC is required for the user to feel high— depending, of course, on who the user is, the set and setting, and the amount he has smoked—but this would be very weak dope. Over 2.5 percent THC qualifies as "good" marijuana, whereas anything higher than about 3.5 percent is considered excellent by almost any standards. In their book on the cultivation of marijuana, Mel Frank and Ed Rosenthal report that the highest THC levels they have come across are 9.7 percent in a sample from Colombia, 13.2 percent in some Mexican marijuana, and 7.8 percent in Hawaiian. These are all very rare readings. Frank and Rosentnal also report having seen some Thai marijuana whose THC level measured in at higher than 20 percent, but they suspected that it had been adulterated with hash oil.[5]
    Each year, the Research Institute of Pharmaccutical Sciences analyzes samples of confiscated marijuana. On the average, marijuana potency increased by about 50 percent between 1973 and 1977. This represents a significant change, but it is a far cry from the charge that there has been a tenfold increase in potency.[6]