844-436-7691
What a New Car-Travel Study Tells Us About Keeping Dogs Calm on the Road
If summer means road trips, vet visits, or a nervous dog who pants and whines the moment the engine starts, you are not alone — and researchers have been paying attention. A blinded, randomized, placebo-controlled study published in Frontiers in Veterinary Science looked at whether cannabidiol (CBD), on its own and combined with two other calming ingredients, could take the edge off the stress dogs feel during car travel. The short version for pet owners: one specific combination measurably blunted the stress-hormone spike, the effects were real but mild, and individual dogs absorbed the CBD very differently. Here is what the science actually shows, graded honestly — including who paid for it.
Evidence Level: 2 of 8 — Randomized Controlled Veterinary Trial
This is a blinded, placebo-controlled, randomized crossover trial in 54 healthy adult dogs — among the strongest study designs veterinary science produces, sitting just below systematic reviews. It can tell us whether a single dose shifted measures of stress under controlled conditions. It cannot tell us how any individual dog will respond at home, how repeated daily dosing compares, or anything about dogs with diagnosed medical conditions.
Who ran it: the study was conducted by researchers at the Waltham Petcare Science Institute in the United Kingdom, which is the research arm of Mars Petcare. That does not invalidate a well-designed trial — the blinding, the placebo control, and the crossover structure are exactly what you want to see. But industry-funded research deserves the same scrutiny we ask you to apply to our own company-commissioned studies, and you should know the affiliation before you weigh the findings. The dogs were also kennel-housed research dogs who had been trained in advance to enter a crate in the car, not pet dogs experiencing a family road trip.
What the researchers actually did
The team worked with 54 healthy adult dogs across three breeds — 19 Norfolk Terriers, 9 Beagles, and 26 Labrador Retrievers, with a mean age of 3.6 years. Using a crossover design (each dog experienced every condition, so each dog served as its own comparison), they gave one of four single treatments about two hours before a standardized ten-minute car journey:
- A placebo
- CBD at 2 mg per kg of body weight
- CBD at 4 mg per kg of body weight
- A blend of CBD at 2 mg/kg plus L-tryptophan and alpha-casozepine, a milk-derived peptide long used in calming supplements (the alpha-casozepine target was a minimum of 20 mg/kg)
Because the study was blinded and placebo-controlled, neither the dogs' handlers nor the assessors knew which treatment a dog had received — the design built specifically to keep wishful thinking out of the results. The researchers tracked both physiological signals (serum cortisol, heart rate, heart rate variability, surface temperature, and blood CBD levels) and behavioral ones (posture, activity, whining, lip-licking, panting, and ear position).
What they found — stated plainly
The clearest result: the CBD-plus-blend treatment produced a significantly smaller rise in cortisol — the body's primary stress hormone — from baseline to after the car ride, compared with placebo (p = 0.016). Neither CBD dose on its own reached statistical significance against placebo: 2 mg/kg came in at p = 0.583 and 4 mg/kg at p = 0.128. In other words, it was the combination, not CBD alone and not more CBD, that moved the needle. The researchers also reported that dogs with higher CBD levels in their blood tended to show better heart rate variability, a marker generally associated with a calmer physiological state.
Equally important is what did not reach significance. Most of the individual behavioral measures showed only non-significant trends (for example, a hint of less lip-licking and lower activity with the blend), and the overall effect sizes were mild. The authors' own summary word was "mild." This was a nudge in the calmer direction under one specific set of conditions — not a switch that flipped anxious dogs into relaxed ones.
The finding that surprised the researchers: absorption varied enormously
Across every treatment, how much CBD actually reached the dogs' bloodstream varied widely — and a number of dogs had CBD plasma levels below the limit of detection even after being dosed. That is a striking result in a controlled facility where dosing was supervised.
Breed appeared to play a role: Norfolk Terriers, the smallest breed in the study, showed lower plasma CBD levels than Labrador Retrievers. Individual animal and breed together accounted for a meaningful share of the variation the researchers modeled.
The authors floated the delivery format as one possible contributor — the CBD in this study was combined with other ingredients and extruded into a treat, and they noted it is possible the manufacturing process limited bioavailability. But they were careful not to overclaim, and so are we: they cited one study finding semi-solid treat formats produce lower peak levels than liquids, and another finding soft-chew pharmacokinetics essentially similar to oil. They also observed dogs with unusually high plasma levels as well as unusually low ones, and concluded that differences in bioavailability were "not the sole cause" of the variation. Diet, meal timing, and individual metabolism are all still on the table.
So the honest takeaway is not "treats don't work and oils do." It is narrower and more useful: the amount of CBD on a label is not the amount that reaches your dog, and the gap between the two is bigger and less predictable than most of the industry admits. That is a real argument for buying from companies that publish batch-specific third-party lab results so you can at least verify what went into the product — and for judging any supplement by how your own dog responds over weeks rather than by the number on the front of the bottle. If you're weighing formats for your own dog, we've written a fuller comparison of CBD oil versus treats for dogs.
Where this sits next to the rest of the evidence — including our own
Calming and travel is one of the better-studied corners of pet cannabinoid research, which is unusual. The Waltham group behind this trial has published related work reporting that CBD influenced measures of stress in dogs during car travel and separation, and a six-month study concluding that daily 4 mg/kg dosing was well tolerated in healthy adult dogs. Worth noting that this is a consistent body of work from a single institute rather than independent replication across labs — a real limitation in a young field. Meanwhile, most marketing claims across the pet-CBD industry still rest on Level 8 evidence: anecdotes and testimonials.
We hold our own research to the same ladder, and to the same disclosure. HempMy Pet commissioned an equine study at Tarleton State University (Texas A&M System) with Dr. Kimberly Guay, Ph.D., examining horses under the stress of transport. In that work, horses receiving our hemp extract showed reduced measures of stress during trailering, with the 0.6 mg/kg dose outperforming 0.3 mg/kg and effects peaking around four hours — a prospective clinical study, which lands at Level 3 on the ladder. Our 90-day canine study on joint comfort with Dr. Robin Downing, DVM, alongside researchers from Colorado State University, is also a Level 3 prospective study. Both were paid for by us. We say so for the same reason we flagged Waltham's affiliation above: placing our own work honestly on the ladder is the entire point. You can read more on our clinical trials page.
Practical takeaways for your next car trip
The research supports a measured, realistic approach to supporting a dog's comfort during travel: think calm and quality of life, not a cure for a diagnosed condition. Give any calming supplement time to be absorbed before stress begins — the study dosed two hours ahead, which lines up with research showing CBD blood levels peak roughly 1.5 to 2 hours after dosing. Expect real individual variation, and don't assume a dose that suits a Labrador suits a terrier. Choose a transparent product with published testing, and pair supplements with the basics that always help: a secured crate or harness, familiar bedding, a pre-trip walk, and short practice drives — remember that every dog in this study had been trained to enter the car crate calmly before testing began. If your dog has a diagnosed anxiety or medical condition, that is a conversation for your veterinarian — supplements support general calm and comfort, they are not a treatment. For a broader look at the topic, see our guide to hemp and CBD for dog anxiety, or explore our hemp for dogs collection to see how our oils are formulated and tested.
Frequently asked questions
Does this study prove CBD calms anxious dogs?
No — and it is worth being precise. It is a strong, randomized, placebo-controlled trial that found one CBD-containing blend reduced the cortisol spike during car travel, with mild overall effect sizes in healthy dogs. It supports the idea that CBD can positively influence measures of stress under controlled conditions. It does not diagnose, treat, or cure anxiety, and it cannot predict how any individual dog will respond.
Why did the combination blend work better than CBD alone in the study?
The blend paired CBD at 2 mg/kg with L-tryptophan and alpha-casozepine, two ingredients independently associated with calming. That combination was the only treatment to significantly reduce the cortisol rise versus placebo (p = 0.016), while CBD alone at either 2 or 4 mg/kg did not. Exactly why is not settled, and the authors called for more research into how CBD interacts with other active ingredients.
How long before travel should a calming supplement be given?
In this study, treatments were given about two hours before the car journey, which matches research showing CBD blood levels tend to peak around 1.5 to 2 hours after dosing. Giving a supplement time to absorb before the stressful event begins is a reasonable, evidence-informed approach — though absorption varies considerably between dogs.
Why do some CBD products seem to do nothing?
The study offers a real clue: absorption varied widely, and some dogs had no detectable CBD in their blood despite being dosed. The researchers pointed to several possible reasons — delivery format, diet and meal timing, breed, and individual metabolism — and were explicit that no single factor explained it. What it means practically is that the number on a label is not the amount that reaches your dog, which is why we publish batch-specific lab results and why judging results over weeks beats judging them over one dose.
Is CBD safe for dogs?
Research on healthy adult dogs, including a six-month daily-dosing study from the same institute behind this car-travel work, has generally reported CBD to be well tolerated at studied doses. As with any supplement, talk with your veterinarian before starting — especially if your dog takes other medications or has a health condition.
About the Author
Written by Marc Brannigan, Co-Founder & CEO of HempMy Pet. Marc founded HempMy Pet in 2016 and built it into a vertically integrated, seed-to-sale organic hemp company — breeding its own hemp genetics, growing them on our own farm in Longmont, Colorado using organic growing practices, and formulating every product in-house. The company has spent nearly a decade formulating hemp products for dogs, cats, and horses and commissioned HempMy Pet's two university clinical trials. More about HempMy Pet → · Our clinical trials →
Sources: Study — Flint HE, Weller JE, Hunt ABG, King T. "Treats containing cannabidiol, L-tryptophan and α-casozepine have a mild stress-reducing effect in dogs," Frontiers in Veterinary Science (2025). Related — Waltham Petcare Science Institute.
This article is for educational purposes only and is not veterinary advice. HempMy Pet products are not intended to diagnose, treat, cure, or prevent any disease. Always consult your veterinarian about your pet's health.
