Introduction
Cannabinoid research has long focused on the central nervous system. Data on interactions with the cardiovascular system and respiratory mechanics remain far more scarce. A randomised clinical trial published on 27 August 2026 in the British Journal of Clinical Pharmacology brings new measurements to this still poorly documented area.
Conducted by a Brazilian team at a university hospital, this research compared, in eighteen healthy adults, the physiological responses observed after oral administration of THC alone, a CBD+THC combination, or a placebo. Heart rate, cardiac output, vascular resistance, electrical activity of the respiratory muscles, and tissue oxygenation: the researchers simultaneously measured a series of parameters rarely brought together in a single protocol.
At The Green Lab, a Swiss laboratory based in Gland since 2017, we follow the scientific literature devoted to hemp and its compounds. This article presents the methodology and results of this publication in a factual manner, without drawing any conclusions about health or product use.
A Study Published in the British Journal of Clinical Pharmacology
The article, entitled Acute effects of THC and a CBD+THC combination on cardiovascular haemodynamics and respiratory muscle activity during loaded breathing in healthy adults, is authored by Edna Karla Ferreira Laurentino, Marina Lyra L. C. Fagundes, Guilherme A. F. Fregonezi and their collaborators. It is published in open access under DOI 10.1002/bcp.70793 and registered in the Brazilian clinical trials registry (ReBEC, RBR-3jsvtbr).
The study received a special research authorisation from ANVISA, the Brazilian health agency, and was approved by a research ethics committee. It was funded in part by CAPES and CNPq, Brazilian public research funding bodies.
The Starting Point: A Lack of Human Data
The authors note in their introduction that the endocannabinoid system — made up of the endocannabinoids 2-AG and AEA, CB1 and CB2 receptors, and the enzymes that produce and degrade them — is not limited to the brain. Its components are also present in the cardiovascular system, the lungs and the pulmonary vessels, in both animals and humans.
Despite this broad distribution, human studies measuring haemodynamic responses and respiratory muscle activity following cannabinoid administration remain limited in number and their results heterogeneous. This gap is what the team set out to document.
How the Study Was Conducted
The principle is straightforward. Eighteen healthy adults — nine women, nine men, with an average age of 26 — visited the laboratory three times, at least 48 hours apart. At each visit, they received one of the three preparations:
| Visit | Contents of the dose |
|---|---|
| THC alone | 12.50 mg of Δ9-THC |
| CBD + THC | 12.50 mg of CBD + 12.50 mg of THC |
| Placebo | Neutral oil, without cannabinoids |
Please note: these quantities are part of a clinical research protocol governed by a specific regulatory authorisation granted by the Brazilian health agency.
No one knew what was being administered — neither the participants, who wore an eye mask and a nose clip to neutralise any odour, nor the people conducting the measurements, nor the statistician. The order of conditions was randomised. This type of design, known as a double-blind crossover trial, offers a valuable advantage: each participant serves as their own point of comparison.
The selection criteria were stringent. No medication, no exposure to cannabis in the six months prior, and a verified normal pulmonary function before inclusion.
How a Session Unfolded
Seated, with a mouthpiece between their lips, each participant completed an eight-minute sequence: two minutes of calm breathing, two minutes breathing against a resistance — comparable to the effort required to blow through a narrow straw — followed by four minutes of recovery.
This sequence was repeated three times per visit: before the dose, then one hour and two and a half hours afterwards. These two time points correspond to the window during which orally ingested cannabinoids produce their most pronounced effects.
What the Devices Recorded
Three families of measurements, all non-invasive, ran simultaneously:
- The heart and circulation, via electrodes placed on the chest: heart rate, the volume of blood ejected with each beat, and the resistance offered by the blood vessels.
- The respiratory muscles, via electrodes placed on the neck, chest and abdomen: the intensity of the electrical activity of four muscles engaged during inhalation.
- The oxygenation of a thigh muscle, via an infrared light sensor that distinguishes oxygen-laden haemoglobin from depleted haemoglobin.
Blood pressure, oxygen saturation and a perceived exertion scale were also recorded at regular intervals.
The Observed Results
Heart and Circulation
Both active oils produced a significant increase in heart rate compared to placebo, on the order of up to 15 beats per minute during the interventions.
In the THC-alone condition, cardiac output — the volume of blood pumped per minute — increased significantly at both one hour and two and a half hours after the dose. At the same time, vascular resistance decreased, a sign of widening circulation. The volume of blood ejected with each beat was also higher in both active conditions compared to baseline measurements.
The authors are careful to place these figures in context: the measured increases of 30 to 40% for cardiac output and 27% for ejection volume correspond to what is commonly observed during light to moderate physical exercise. They note that while these variations are statistically significant, they remain well below the adjustments seen during aerobic exercise, and describe them as transient physiological adaptations in healthy adults.
Respiratory Muscles
In the THC-alone condition, the neck and chest wall muscles involved in inhalation worked more intensely during respiratory effort, at one hour and two and a half hours after the dose. The abdominal muscle measured showed no difference.
In the CBD+THC condition, the increase was limited to two of these muscles, with a profile the authors describe as more attenuated and closer to that of the placebo.
The authors urge caution here. This type of electrode captures a signal influenced by many factors: the variations should be read as an indirect indicator of muscle activation, not as proof of a change in the nervous control of breathing.
Muscle Oxygenation
The infrared sensor placed on the thigh recorded, in the THC condition, higher levels of oxygen-laden haemoglobin and lower levels of depleted haemoglobin, particularly during respiratory effort and recovery. With one exception, these variations remained below the threshold of statistical significance: the authors describe them as a trend, not an established finding.
What Participants Experienced
A standardised questionnaire, completed before the dose and then one and two hours afterwards, revealed no significant difference between the three conditions: all values remained in the low range of the scale.
Regarding reported symptoms: 76% of participants reported nothing under placebo. In the CBD+THC condition, 40% reported drowsiness, 20% dizziness, 10% thirst, 10% nausea, 7% difficulty concentrating and 3% blurred vision. In the THC-alone condition, 35% reported drowsiness, 22% dizziness, 9% excessive hunger and 4% significant thirst. No serious adverse effects were reported.
What the Authors Conclude — and the Limits They Acknowledge
The researchers’ conclusion is measured: acute administration of THC and CBD+THC produced distinct cardiorespiratory responses in healthy individuals, with THC alone generating a more pronounced profile and the CBD+THC combination a more attenuated one.
They immediately clarify that the specific effect of CBD cannot be isolated, since the protocol did not include a CBD-alone arm. The other limitations they identify are numerous and worth citing:
