The marijuana that is available today may be much more potent than marijuana cultivated in the past, according to the results of new tests.

The psychoactive component in the marijuana plant is the chemical THC, and the new tests showed that today's marijuana may contain 30 percent THC, Andy LaFrate, the author of the new report, said in a statement.

By contrast, THC levels in marijuana 30 years ago were lower than 10 percent, said LaFrate, who is the president and research director at Charas Scientific, one of eight labs certified by the state of Colorado to conduct marijuana potency testing.

"As far as potency goes, it's been surprising how strong a lot of the marijuana is," LaFrate said. He called 30 percent a "huge" number.

At the same time, the marijuana samples tested had very low levels of a compound called cannabidiol, or CBD, that is touted for its medicinal properties. In fact, some samples did not contain any of this compound. [11 Odd Facts About Marijuana]

Researchers are investigating CBD for its potential in treating people with schizophrenia, Huntington's disease and Alzheimer's disease.

Still, even marijuana with low or nonexistent CBD levels has medicinal properties, said Anthony Fabrizio, a marijuana chemistry expert at Terra Tech Corp, a California agricultural company focused on local farming and medical cannabis.

"Cannabinoids are a single component of what is active in the medicinal properties of [marijuana] plants," Fabrizio said.

Multiple other compounds contribute to these properties, working "synergistically together, almost like a football team," he said.

LaFrate also said that although users can now choose from hundreds of strains of marijuana, the strains might have similar levels of THC and CBD.

"The absolute amount of cannabinoids might change, which relates to strength" or potency of the plant, he said. "But the ratio of THC to CBD to other cannabinoids isn't changing a whole lot." 

As a result, there may not be much difference in how individual varieties of pot make users feel, despite claims that one variety makes people feel mellow, while another one makes them feel alert, he said.

But Fabrizio disagreed. In addition to cannabinoids, another class of compounds also affects the range of sensations a user may experience from smoking marijuana, he said.

The compounds in this class are called terpenes, and they are responsible for pot's unique smell. "The feelings [resulting from using marijuana] vary by a huge amount, because what we are really changing from strain to strain is that terpene profile," he said.

In his analysis of marijuana samples, LaFrate also found traces of fungi and contaminants such as heavy metals, and butane, a compound that is used to create marijuana extracts. It is not clear what a safe level of these substances might be, or which contaminants deserve concern, he said.

The new research was presented today (March 23) at the 249th National Meeting & Exposition of the American Chemical Society.

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