Dec. 1 (UPI) -- Drivers who vape a combination of THC and CBD or THC alone show signs of "modest" impairment up to four hours later, a study published Tuesday by JAMA found.
The impairment from vaping compounds containing the main ingredients of marijuana is equivalent to that seen in drivers with blood alcohol concentrations of 0.05%, or roughly half the legal limit for driving under the influence in most states, the researchers said.
Compounds containing higher amounts of tetrahydrocannabinol, or THC, "are typically used for intoxication," while those with cannabidiol, or CBD, which are not intoxicating, are prescribed for the treatment of epilepsy, anxiety, psychosis and neurological disorders, they said.
While researchers in the new study had participants vape cannabis oil, previous studies have linked any marijuana consumption -- smoking flower, vaping or using edibles, among other methods -- to a higher risk for car accidents.
"[Our] study shows that cannabis-induced driving impairment varies with cannabis strains," study co-author Dr. Johannes Ramaekers told UPI.
"The implication for the general public is that the cannabis-induced driving impairment should be acknowledged as a public health risk, while taking into account that impairment may differ between cannabis strains and depends on time after use," said Ramaekers, professor of psychopharmacology and behavioral toxicology at Maastricht University in the Netherlands.
Because of its medicinal value, the sale of CBD-based products is legal in all 50 states, though some states require a doctor's prescription, according to the non-partisan research web site ProCon.org.
Meanwhile, 33 states have legalized "medical marijuana" that contains both THC and CBD, and 15 states, as well as Washington, D.C., allow the drug to be used for both medical and recreational purposes, the site says.
Although some studies have linked CBD use with increased accident risk while driving, its effect on driving performance remains unclear, Ramaekers and his colleagues said.
For this study, 22 adults completed eight, 60-mile on-road driving tests 40 minutes and four hours after cannabis consumption.
Some participants used vaping devices containing either 13.75 mg each of THC and CBD, 13.75 mg of THC alone or 13.75 of CBD alone, while others were given a placebo containing neither of the ingredients, the researchers said.
These amounts are roughly equivalent to the levels found in one-third of a marijuana cigarette or "joint," according to industry publication High Times.
Participants' driving was evaluated based on standard deviation of lateral position -- a standard measure of "lane weaving" -- the researchers said.
At 40 to 100 minutes following consumption, standard deviation of lateral position was 7.2 inches with CBD-dominant cannabis, 8.1 inches with THC-dominant cannabis, 8.3 inches with THC/CBD-equivalent cannabis and 7.2 inches with a placebo, the data showed.
At four to five hours following consumption, standard deviation of lateral position was 7.5 inches with CBD-dominant cannabis, 7.8 inches with THC-dominant cannabis, 8.1 inches with THC/CBD-equivalent cannabis and 7.6 inches with placebo cannabis.
In general, impairment following cannabis use "was modest in magnitude" and similar to that seen in drivers with a 0.05% blood alcohol content, they said.
Still, even with this "modest" impairment, "driving after consumption of THC dominant cannabis is not safe [and] CBD-induced driving impairment might occur at high doses," Ramaekers said.