CBD May Worsen Adverse Effects Of THC In Edibles, Johns Hopkins Scientists Warn

While it is often considered that CBD can mitigate some of the negative effects of THC, a new study shows the contrary when it comes to marijuana edible products.

According to the new research from Johns Hopkins Medicine scientists, published in JAMA Network Open, CBD inhibits the metabolism, or breakdown of THC, which can cause stronger and longer-lasting cannabis effects — including adverse ones.

20 Times More THC

The clinical trial, which included 18 adult participants ingesting 20 milligrams of Delta 9-THC plus 640 milligrams of CBD, resulted in "stronger subjective drug effects" and "greater impairment of cognitive and psychomotor ability."

Participants also experienced a greater increase in heart rate relative to 20 milligrams of Delta 9-THC alone and placebo.

The maximum concentration of THC measured in participants’ blood was nearly twice as much after consuming a brownie with both THC and CBD, versus a THC-only brownie, even though the amount of THC was the same (20 milligrams) in each edible, writes Medical Xpress.

Furthermore, the maximum amount of metabolic byproducts of THC that causes a similar effect of THC (11-OH-THC) was 10 times higher after eating edibles with high concentrations of CBD than after consuming edibles containing only THC extract.

The Importance Of Consumption Method 

"The fact that THC and CBD were orally administered was very important for the study, and played a large role in the behavioral effects and drug interactions we saw," said Austin Zamarripa, a postdoctoral research fellow at the Johns Hopkins University School of Medicine and the study's lead author.

Most of the previous studies that were trying to assess how CBD and THC combined are affecting our bodies and mind used other methods of consumption — by inhalation or intravenously.

A recent experimental study published in Addiction and led by UCL and King's College London revealed that the short-term effects of vaporized cannabis are the same on both adolescents and adults, and cannabidiol or CBD does not mitigate “the acute harms caused by delta-9-tetrahydrocannabinol.” This study analyzed only vaporized marijuana effects.

One study, published in the Journal of Psychopharmacology in May 2022, shows that CBD can minimize some of the negative effects THC has on the brain. This study used vaporization as the method of consumption.

"Cannabis is a very popular recreational drug, and is also starting to be used medically for some purposes, but we still don’t know a great deal about how different cannabinoids affect the brain," study author Matt Wall, a senior imaging scientist at Invicro, told PsyPost at the time. The researchers revealed that THC and CBD have opposing effects.

This means that most of the previous findings on interactions of THC and CBD may not be applicable to edible cannabis products like cookies and other baked goods, candies, and gummies, which are all metabolized in the intestine and liver.

Stronger, Longer-Lasting Effects, Impairments

"Overall, we saw stronger subjective drug effects, greater impairment of cognitive [thinking] and psychomotor [moving] ability and greater increase in heart rate when the same dose of THC was given in a high CBD cannabis extract, compared with a high THC extract with no CBD," Zamarripa added.

In this study 18 adults (11 men and 7 women) took part, all of which who had not consumed marijuana for a minimum of 30 days before taking part in the research.

They were also given a drug cocktail with five cytochrome (CYP) probe drugs (100 milligrams caffeine, 25 milligrams losartan, 20 milligrams omeprazole, 30 milligrams dextromethorphan, and 2 milligrams midazolam) 30 minutes after consuming each edible. This was for the purpose of analyzing how CBD and THC impact how we metabolize other common drugs and dietary supplements. These findings are yet to be revealed in a separate paper.

With the DEQ tool, participants graded subjective drug effects on a scale from zero to 100, with zero meaning “not at all affected” and 100 being “extremely affected.” The ratings revealed the following subjective impacts:

• Overall drug effects: 59 (THC only) vs. 73 (THC+CBD)
• Unpleasant drug effects: 20 (THC only) vs. 39 (THC + CBD)
• Feeling sick: 12 (THC only) vs. 26 (THC + CBD)
• Dry/red eyes: 16 (THC only) vs. 29 [THC + CBD)
• Troubles with performing routine tasks: 30 (THC only) vs. 47 (THC + CBD). 

Scientists also discovered that participants had higher memory and attention impairments, and a much higher heart rate (from 10 to 25 beats per minute increase from baseline) when consuming edibles with both CBD and THC.

"We have demonstrated that with a relatively high oral dose of CBD [640 milligrams] there can be significant metabolic interactions between THC and CBD, such that the THC effects are stronger, longer-lasting, and tend to reflect an increase in unwanted adverse effects," said Ryan Vandrey, professor of psychiatry and behavioral sciences at the Johns Hopkins University School of Medicine and the study's senior author.

People should consult their doctors and be careful when taking a high-dose CBD extract in combination with other medications, Vandrey warns.

The scientists concluded that more studies are needed to complete the understanding of CBD and THC interactions.

Photo: Courtesy of Elsa Olofsson on Unsplash