CBD Increased THC's High and Blood Levels, While Caffeine Had Minimal Impact | Research

The takeaway

In a crossover study of 20 adults, CBD co-administration increased THC's subjective high, performance impairment, and plasma THC concentrations, while caffeine had minimal effects on THC.

cannabis product regulators, pharmacologists, consumers of CBD+THC products, drug interaction researchers

What the researchers found

Caffeine produced minimal changes in THC-induced subjective effects, performance, or metabolism, though signals for perceived driving impairment were observed. CBD, co-administered with THC and caffeine, increased abuse-liability outcomes (drug high, p=0.002), performance impairment, and plasma THC (p=0.004) and 11-OH-THC (p<0.001) concentrations compared to THC alone.

Why it matters

Cannabis products premixed with caffeine are increasingly common but have never been studied. The unexpected finding that CBD increases THC's effects and blood levels challenges the common belief that CBD moderates THC's impact.

The numbers in context

20 participants (10M/10F). THC: 7.5 mg. Caffeine: 180 mg. CBD: 105 mg. CBD increased: drug high (p=0.002), plasma THC (p=0.004), 11-OH-THC (p<0.001). Caffeine: minimal THC effects. CBD increased performance impairment vs. THC alone.

How the study worked

Double-blind, randomized, placebo-controlled, within-subject crossover study. 20 participants (10 men/10 women) completed outpatient sessions with oral THC (7.5 mg), caffeine (180 mg), and/or CBD (105 mg) in cumulative dosing design. Outcomes: subjective effects, simulated driving, plasma concentrations.

What this study cannot tell us

Small sample (20). Oral administration only, not smoking or vaping. Specific doses may not represent commercial products. Single-session acute effects. Cannot determine chronic co-administration effects.

How to read the evidence

Well-designed crossover RCT with pharmacokinetic data, though small sample limits to moderate.

When this study was published

Recently published controlled pharmacology study.

The bigger picture

The finding that CBD increases THC's high and blood levels has major implications for product labeling, dosing guidance, and the popular narrative that CBD 'balances out' THC. It also highlights the importance of considering full cannabinoid profiles in regulation.

Questions still open

Does CBD always increase THC effects, or is this dose-dependent?
Should cannabis product labels warn about CBD-THC interactions?

Common questions

Does CBD reduce THC's effects?

Contrary to popular belief, this study found CBD increased THC's subjective high, performance impairment, and blood levels when taken together orally. CBD may not be the moderating influence it is commonly thought to be.

Does caffeine change how THC affects you?

Caffeine had minimal impact on THC's effects in this study, despite the increasing availability of cannabis-caffeine combo products.

Read the original research

Effect of caffeine and cannabidiol (CBD) co-administration on Δ9-tetrahydrocannabinol (Δ9-THC) subjective effects, performance impairment, and pharmacokinetics.

Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology, 50(12), 1827-1835

View on PubMed ↗Publisher’s paper ↗

Citation

Strickland, Justin C; Tilton, Hayleigh E; Patton, Noah M; Vandrey, Ryan; Austin Zamarripa, C; Spindle, Tory R; Lee, Dustin C; Bergeria, Cecilia L; Wolinsky, David; Klawitter, Jost; Sempio, Cristina; Campos-Palomino, Jorge; Christians, Uwe; Feldner, Matthew T; Irons, Jessica G; Bonn-Miller, Marcel O. (2025). Effect of caffeine and cannabidiol (CBD) co-administration on Δ9-tetrahydrocannabinol (Δ9-THC) subjective effects, performance impairment, and pharmacokinetics.. Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology, 50(12), 1827-1835. https://doi.org/10.1038/s41386-025-02232-x