Perhaps teenagers who develop schizophrenia are four times more likely to smoke marijuana?

For one, the fact that marijuana is much more potent than it was just ten or fifteen years ago. Not just by a small margin, but by a huge leap. THC levels can be as high as 20% or more. Something jamie spoke of, the odd feeling it gives him, especially the sativas. They feel unnatural, because growers have altered the plant to produce more THC.

The highest tested sample had 22.04% THC (domestic) and 27.30% THC (nondomestic). The highest tested sample ever tested between 1975 and 2009 had 33.12% THC (domestic) and 37.20% THC (nondomestic).

After a careful consideration of historical records, reports of recent potency estimates, and the practice of marijuana smokers to self-adjust their dose, the authors reached the following conclusion.

"While it may be true that sinsemilla is more widely available than 10 or 15 years ago, its potency has not changed significantly from the 2.4 to 9.5 percent THC materials available in 1873-1974, or the five to 14 percent sinsemilla of 1975. The range of potencies available then (marijuana at 0.1% to 7.8% THC, averaging 2.0% to 5.0% THC by 19750 was approximately the same as reported now. With such a range, the evidence simply cannot support the argument by Cohen that marijuana is "ten or more times more potent than the product smoked ten years ago." And to say that marijuana potency has increased 1,400 percent since any date in history is patent nonsense."

"It is not legitimate to imply that average low potencies represent the full range of potencies available in reality. Neither is it valid to cite the low end of the range then as a baseline to compare the high end of the range now. The claimed baseline for THC content in the early 1970's would appear to be too low, probably because confiscated stored police samples were utilized; and this low baseline makes the claimed difference in potency appear to be greater than it has been in reality."(31) (emphasis in original)

An examination of the government's actual potency data (rather than what they have reported in press releases) was conducted by Dr. John Morgan of the City University of New York Medical School, and indicated that the finding was based on a comparison of the highest THC percentage in the 1980's with the lowest percentage of the 1970's. Also, the data from the 1970's was derived from a sample of decaying, imported Mexican marijuana composed of leaf and flower; it was compared to recently harvested, domestically grown marijuana flowers. Finally, marijuana of similar potency to 1980's standards was available during the 1970's. (32)

Morgan's debunking of marijuana potency findings relies on data presented by the NIDA potency project at the University of Mississippi. This data shows that the arithmetic average potency of domestic cannabis tested by the project has ranged from 1.5% to 4.75% THC. (33) In 1973 Gabriel Nahas reports that the THC content of drug-type cannabis ranges from 3.4 to 4.8%. (34) In 1975, before the emergence of high quality domestic marijuana cultivation in the U.S., John Langer of the DEA reports that:

"Marihuana produced in the United States is considered inferior because of the low concentration of psychoactive ingredients, which varies between 0.2 and 2.0 percent. Marihuana of Mexican origin is known to be slightly stronger. The variety known as Jamaican ganja, which consists primarily of the flowers and breacts, has a THC content of 4 to 8 percent."(35)

These citations from Nahas and the DEA independently demonstrate that a broad range of marijuana potencies was available in the 1970's, and provide additional evidence that assertions otherwise are without factual or scientific foundation.

It is important to understand the fallacy of the increased potency argument for several reasons.

1) It is just wrong. It is factually incorrect.

2) It is ironic that advocates of marijuana prohibition claim prior research is inadequate to explain the effects of this new, high potent marijuana when as explained in section 3, most of the contemporaneous research was later criticized for using extremely unrealistic potencies.

3) It is convenient. The hypothesis that marijuana is now much more potent than in the past provides convincing support for the assertion that any use of the drug is drug abuse. Rhetoric about marijuana potency substitutes for scientific findings in efforts to legitimize existing policy.

4) Most importantly, the scientific research reported in section 3 renders the potency question irrelevant to an assessment of the acute and chronic effects of marijuana use. Remember, in the mid 1980's when this hypothesis gained popularity, the dominant research paradigm was (incorrectly) based on cell membrane perturbation. Certainly, if marijuana produced dangerous effects by toxic seepage into cell membranes, than increases in potency represent increases in danger. Certainly if marijuana produced tolerance by desensitizing brain cells, a result of this toxic seepage, then increases in potency would increase the danger of adverse effects. However marijuana produces its results by way of a neural receptor system, not membrane perturbation, and the brain can tolerate extremely high potent doses of cannabinoids. Tolerance to marijuana develops through receptor down-regulation; the body's response to high potency marijuana is seek a manageable equilibrium through receptor down-regulation. The potency hypothesis may have had some relevance in the 1980's, regardless of its foundation. However in the 1990's, the potency hypothesis has neither foundation nor relevance.