Marijuana legalization opponent Heidi Heilman says today's marijuana is 300 percent to 800 percent stronger than in the past

Editors note: This item was revised on April 1, 2014 to reflect the fact that increases of 300 and 800 percent represent four- and nine-fold increases respectively. The ruling remains the same.

In the debate over whether marijuana should be legalized, one issue is the question of potency. Critics of legalization argue that the street drug now available for sale is not the marijuana that a lot of baby boomers and Generation Xers have used.

One of them, Heidi Heilman, director of New England field development for Smart Approaches to Marijuana and president of the Massachusetts Prevention Alliance, raised the issue March 13 in a commentary in The Providence Journal.

"Today’s marijuana is 300 percent to 800 percent more potent than the pot of yesteryear," she wrote. "Such dangerous levels of THC heighten mental illness and addiction risks for those who smoke marijuana — especially for kids with developing brains."

THC or tetrahydrocannabinol, available by prescription, is the key active ingredient in marijuana.

It's well established that the potency of marijuana has increased over time. On Jan. 24, PolitiFact national ruled that when former Rhode Island Congressman Patrick Kennedy said that marijuana today is "genetically modified," with THC levels that "far surpass the marijuana" of the 1970s, his statement was Mostly True.

Heilman was being more specific. Because something 100 percent more potent is actually twice as potent, she was saying that the potency of today's marijuana is now four to nine times greater than "yesteryear," a rather vague starting point. Nonetheless, we wanted to see if her statement was on target or her statistic was a bit high.

Heilman was quick to send us several pieces of information.

The first was a graph showing a rapid increase in potency from 1960 to 2011, a 52-year span. It shows the ratio of THC in marijuana going from 0.2 percent to 11.4 percent. That's an increase of 5,700 percent, well outside the range cited by Heilman.

But are those numbers reliable?

The graph says the information came from a study in the Journal of Forensic Science. But that study was published in 2010, and only covered a 16-year period that ends in 2008.

Its authors, researchers at the National Center for Natural Products Research at the University of Mississippi, examined 46,000 samples of marijuana seized during law enforcement raids. They found that the THC concentrations of marijuana had risen by about 171 percent in that time period, well below the 300 to 800 percent increase cited by Heilman.

We also contacted the Drug Enforcement Administration in Boston and Washington and the White House Office of National Drug Control Policy. They referred us back to the research center at Ole Miss, which has been monitoring THC content at least since the early 1970s.

The researchers there sent us copies of their reports, all published in the journal, along with test results that included the most recent data. We also secured some of their quarterly reports.

We found that even though the report Heilman cited didn’t back up her claim, the Ole Miss data did.

YEAR

Tested

% THC

YEAR

Tested

% THC

YEAR

Tested

% THC

1972

34

0.18

1986

1370

2.36

2000

3148

4.92

1973

33

0.22

1987

1550

2.96

2001

2716

5.36

1974

114

0.36

1988

1640

3.18

2002

2413

6.4

1975

149

0.48

1989

1075

3.04

2003

2517

6.31

1976

209

0.98

1990

1108

3.24

2004

2637

7.24

1977

251

1.76

1991

2148

3.09

2005

3004

7.24

1978

130

1.73

1992

3336

3.08

2006

2891

7.76

1979

220

1.53

1993

3031

3.38

2007

3114

8.74

1980

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151

2.15

1994

3024

3.50

2008

2775

8.89

1981

249

2.11

1995

4792

3.77

2009

3079

8.34

1982

435

3.07

1996

2451

4.09

2010

2720

10.7

1983

1145

3.30

1997

2496

4.64

2011

2342

11.13

1984

1030

3.31

1998

2283

4.47

2012

2055

12.3

1985

1449

2.83

1999

2692

4.6

In 2012, the most recent year in which testing has been completed, the average THC concentration was 12.3 percent.

That would be 300 percent higher (or four times stronger) than 1992 levels, when the average was 3.08 percent. And it would be 800 percent higher (or nine times stronger) than the average level of 0.98 percent found in 1976.

How high could the THC content potentially go?

One specimen, seized on Sept. 11, 2007, was found to have a THC content of 37.2 percent.

Our ruling

Heidi Heilman said, "Today’s marijuana is 300 percent to 800 percent more potent than the pot of yesteryear."

Long-term testing shows that, on average, today's marijuana is three times more potent than pre-1993 marijuana and eight times more potent than grass seized in 1976 and earlier.

We rate her claim as True.

(If you have a claim you’d like PolitiFact Rhode Island to check, email us at [email protected]. And follow us on Twitter: @politifactri.)