Regular cannabis users experienced significantly fewer early or extra heartbeats on days they smoked or vaped compared with days they abstained, according to the results of a new trial published in the Journal of the American College of Cardiology.

The study, led by researchers at the University of California, San Francisco (UCSF), tracked 108 adults who regularly smoked or vaped cannabis but had no history of diagnosed heart rhythm problems. Over 14 days, each participant was randomly told to either inhale cannabis or abstain. During the study, they wore a monitor that continuously recorded their heartbeat, alongside an activity tracker, sleep monitor and glucose monitor. Because each participant switched between cannabis and abstinence days, they effectively acted as their own control group, letting researchers compare the two conditions directly.

On the days participants used cannabis, they had about 9% fewer premature heartbeats than on the days they didn’t – the opposite of what the research team predicted.

“We were surprised by the results because they contradicted our original hypothesis,” said Gregory Marcus, the study’s senior author and an endowed professor in atrial fibrillation research at UCSF’s Division of Cardiology. “That’s why randomised trials are so important. When the data challenge our expectations, our job as scientists is to understand them, not ignore them.”

Early or extra heartbeats – known clinically as cardiac ectopy – are common, and can originate in either the heart’s upper or lower chambers. The improvement seen in this trial was driven entirely by fewer premature atrial contractions (PACs), the type that begin in the upper chambers and are considered the strongest known predictor of atrial fibrillation, a rhythm disorder linked to blood clots and stroke. There was no meaningful change in premature ventricular contractions (PVCs), which begin in the lower chambers and are linked to future heart failure risk instead.

The monitors also picked up no meaningful differences in how much participants slept, how many steps they took, or their blood sugar levels between cannabis and abstinence days – ruling out some of the more obvious explanations for the effect.

Marcus was careful to stress that the findings shouldn’t be read as a green light. “The overall health effects of inhaled cannabis may still be net negative, but these findings suggest there may be something about cannabis that can teach us more about the biological mechanisms that produce premature atrial contractions,” he said. “That knowledge could eventually lead to new approaches for preventing or treating abnormal heart rhythms.”

He added that the trial only looked at short-term, acute effects in existing regular users, not the long-term consequences of cannabis use, and that it “is not sufficient” on its own to change clinical guidance.

Most previous research linking cannabis to heart problems has relied on self-reported use or medical records gathered after the fact, making it hard to separate cause from coincidence. This trial’s randomised, crossover structure – swapping each participant between cannabis and abstinence days rather than comparing separate groups of users and non-users – is considered a far more reliable way of isolating cause and effect.

A 2025 study tracking more than 4,000 US military veterans with existing heart disease found no increased rate of heart attacks, strokes or cardiovascular death among those with a history of cannabis smoking, despite researchers initially expecting the opposite.

Randomised studies “are the only way to fully avoid confounding effects that interfere with revealing underlying realities…that are so common in the majority of observational research,” Marcus added.

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In the first double-blind, placebo-controlled trial, vaporised cannabis was found to be more effective for treating acute migraine symptoms than a placebo.

While preclinical and retrospective studies have suggested cannabinoids may be effective in migraine treatment, according to the researchers, until now, there have been no randomised clinical trials examining these effects in adults with acute migraine symptoms.  

The randomised, double-blind, placebo-controlled crossover trial – widely considered the gold standard in clinical research – involved 92 participants, of which 83% were female. 

Individuals were treated for up to four separate migraine attacks – 247 migraine attacks in total – with vaporised THC-dominant, CBD-dominant, and a balanced CBD/THC cannabis flower, alongside a placebo.

Researchers specifically examined the effects of each type of cannabis on pain relief, as well as complete freedom from pain, and the participants’ ‘most bothersome symptoms’.

The results, published in the journal Headache: The Journal of Head and Face Pain, found that participants who used a combination of THC and CBD reported significant pain reduction and improvement in their ‘most bothersome symptom’ within 2 hours of treatment.

Around 67% of people reported meaningful pain relief with cannabis containing a balance of THC and CBD, compared to 47% with a placebo, with around 60% reporting complete pain freedom, compared to 35%. 

Freedom from the most bothersome symptoms, such as nausea and light sensitivity, was also achieved more often with the balanced cannabis (60%) than with the placebo (35%).

No serious adverse events were reported, and benefits were sustained at 24 and 48 hours.

The THC-dominant cannabis was also superior to placebo for pain relief, with 68.9% of participants, compared to 46.6%, but not pain freedom or most bothersome symptom freedom at the two-hour mark.

Meanwhile, CBD-dominant cannabis was not superior to the placebo for pain relief, pain freedom, or most bothersome symptom freedom.

READ MORE: Could cannabis inhalation help with migraine management?

“First compelling evidence” for cannabis in migraine treatment 

The researchers say the findings suggest that a vaporised, balanced cannabis flower may be a viable treatment for acute migraine in patients who do not respond to standard therapies.

Speaking to Medscape, the study’s senior author, Dr Nathaniel M. Schuster, a pain/headache neurologist, said: “This is the first placebo-controlled study in this space. It’s the first real — to—me—compelling evidence for the antimigraine effects of cannabis in humans.

The authors also argue that the fact that the study was conducted independently from the industry strengthens its findings, although more large-scale, long-term studies on benefit and risk are still needed.

“In this first randomized, double-blind, placebo-controlled trial testing the efficacy of cannabinoids for the acute treatment of migraine, vaporized 6% THC + 11% CBD cannabis flower was superior to placebo for pain relief, pain freedom, and MBS freedom at 2 h as well as 24-h sustained pain freedom and sustained MBS freedom and 48-h sustained MBS freedom,” the authors wrote.

“Strengths of the study include that it was a randomized, double-blind, placebo-controlled study conducted with foundation funding and cannabis from the NIDA DSP and without industry involvement. However, this also limits the generalizability of the study’s findings to commercial products used by patients in real-world settings.”

They add: “Future research should include multicenter RCTs and long-term studies of benefits and risks with repeated use.”

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