An 18-month registry study of 130 autistic adults found that participants reported lower anxiety and better sleep soon after beginning prescribed medical cannabis. The findings are observational, however, and cannot show that cannabis caused the changes.
The participants started treatment at private UK clinics and completed questionnaires before treatment and at one, three, six, 12 and 18 months. The study used the GAD-7 anxiety questionnaire, the Single-Item Sleep Quality Scale and the EQ-5D-5L quality-of-life measure.
Early anxiety improvement was not fully sustained
Average GAD-7 scores fell from 13.5 before treatment to 8.9 after one month. The average score then rose gradually, reaching 10.8 at 18 months.
The study defined a four-point reduction as the minimum clinically important difference. The average improvement remained above that threshold through six months, but was 3.4 points at 12 months and 2.8 points at 18 months.
Sleep ratings also improved early, rising from 3.7 out of 10 at baseline to 5.3 after one month. The average score was 4.8 at 18 months. The largest average improvement was 1.8 points, below the study’s 2.6-point threshold for meaningful change.
Quality of life rose while mobility did not change
The EQ-5D-5L health-related quality-of-life index increased from 0.43 at baseline to 0.58 at three months, then stood at 0.51 at 18 months. Mobility scores did not change significantly.
These measures describe participants’ reported experiences; they do not establish that treatment produced the changes.
THC exposure increased over time
The median daily THC dose rose from 20 milligrams at baseline to 100 milligrams after one month, 152 milligrams at six months and about 192 milligrams at 18 months. CBD doses stayed around 20 to 30 milligrams per day after the first month.
Dried flower alone was the most common prescription product, used by about half the group at each time point. The researchers suggested that inhaled flower, clinician titration and tolerance might help explain the rising THC doses and the later reduction in anxiety and sleep benefits. Those explanations were not established as causes.
Adverse events were reported by a minority of participants
Twenty-five participants reported a combined total of 232 adverse events, while 105 reported none. Of the reported events, 88 were rated mild, 99 moderate, 42 severe and three life-threatening or disabling.
The most common events were insomnia, dry mouth, lethargy, trouble concentrating and fatigue. The study found no clear association between side effects and age, sex, previous cannabis use, route of use, or THC or CBD dose.
Why the results are difficult to interpret
This was an uncontrolled case series. It had no placebo or comparison group, randomization or blinding, so improvements could reflect expectation, natural changes in symptoms or the possibility that participants began treatment when symptoms were particularly severe.
The group also had substantial prior cannabis exposure: 90 participants were already using non-prescribed cannabis, 22 were former users and 18 had never used it. People who already believe cannabis helps them may be more likely to seek a prescription, which could make benefits appear larger.
The participants had an average age of 34; 88 were men and 42 were women. No children were included. Eighty-four participants, or 65%, also had anxiety or depression. Outcomes were self-reported using general questionnaires, with no autism-specific or clinician-rated outcome measure.
The fact sheet does not report how many participants completed each follow-up. When a participant skipped a questionnaire or stopped treatment, researchers filled in the pre-treatment score. The registry came from one private, self-funded clinic network, and patients paid for treatment. Curaleaf Clinic privately owns the registry, most authors list it as an affiliation and Curaleaf products were the most frequently prescribed, although the paper declared no conflicts of interest.
What the study does—and does not—show
The registry adds information about how autistic adults using prescribed cannabis reported anxiety, sleep and quality of life over time. It does not demonstrate that cannabis is an effective treatment for those outcomes, establish the long-term safety of the reported THC exposure or show whether the findings apply to autistic children or to people with different treatment histories.
The study team reported that no randomized controlled trial of cannabis-based medicinal products had been conducted in autistic adults. Evidence from controlled studies in children and young people was described as mixed and insufficient, and those studies used CBD-dominant products rather than the high-THC dried flower used by most adults in this registry.
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