Can Cannabis Make ADHD Worse? What the Evidence Says About the Risks

The evidence and experiences around medical cannabis, ADHD and autism will be explored at the Cannabis Health Symposium in London on 26 November 2026, where a dedicated panel will examine what we know – and where the gaps remain.

Ahead of the event, Cannabis Health explores what we actually know about the risks – and whether cannabis makes ADHD worse. 

Cannabis and ADHD symptoms

A 2026 study led by Sarah Ryan and published in the Journal of Attention Disorders surveyed 900 adults diagnosed with ADHD about their cannabis use and its perceived effects on their symptoms in 2023.

Three-quarters said they had used cannabis at some point in their lives, while 41% had used it in the previous 30 days. Among those who had ever used cannabis, 42% said they had done so to manage ADHD symptoms.

Daily users were more likely than those who used cannabis less frequently to report improvements in “mental frustration” and “impulsivity”.

But they were also more likely to say their “inattention” had become worse.

The researchers concluded that participants reported “mixed effects” on ADHD symptoms and anxiety and called for “further research”.

This was an anonymous online survey rather than a clinical trial – and clinical research into cannabis as an ADHD treatment is even more limited.

As Cannabis Health has examined in its guide to medical cannabis for ADHD, only one small randomised controlled trial has tested a cannabis-based medicine specifically for ADHD.

The 2017 randomised controlled trial led by Ruth Cooper and published in European Neuropsychopharmacology involved just 30 adults, who were given either Sativex – a cannabis-based medicine containing equal amounts of THC and CBD – or a placebo for six weeks.

The trial did not find a significant improvement in its main measure, which looked at cognitive performance and activity levels. There were signs of improvements in hyperactivity and impulsivity and some other measures, but these did not remain statistically significant after the researchers accounted for the number of different comparisons being made.

The researchers described the findings as “preliminary evidence” and said a “larger trial is warranted”.

Almost a decade later, evidence from larger controlled trials remains lacking.

A 2023 study led by Pim Ittiphakorn and published in Neuropsychopharmacology Reports followed 68 ADHD patients prescribed cannabis-based medicines through the UK Medical Cannabis Registry for up to 12 months.

Researchers found improvements in anxiety and sleep, as well as quality of life at some follow-up points, but stressed that “a causative effect cannot be proven”.

Cannabis use disorder and ADHD

One of the clearest potential risks identified in the research is the relationship between ADHD and cannabis use disorder (CUD) – where cannabis use becomes difficult to control and starts causing problems in someone’s life.

A 2024 meta analysis led by Emma Froude and published in the Journal of Psychiatric Research analysed 14 studies examining how common CUD was among people with ADHD.

It estimated that 26.9% had experienced CUD at some point in their lives, while 19.2% currently met the criteria. Overall, people with ADHD were around three times as likely to have CUD as the general population.

The researchers said the findings highlighted the need for people with ADHD to be screened for CUD.

A separate 2024 study led by René Nielsen and published in Nature Mental Health found shared genetic factors between ADHD and CUD.

Among people with ADHD with the highest genetic risk scores for CUD, the chance of having both conditions reached 22%, compared with 1.6% among controls.

However, this does not mean ADHD causes CUD, or vice versa. The study identified shared genetic factors which may help explain why the two conditions frequently occur together.

The 2025 study led by Sarah Ryan and published in the Journal of Attention Disorders also found differences depending on how frequently adults with ADHD used cannabis.

Daily users had higher rates of CUD and were more likely to have diagnoses including anxiety, depression, bipolar disorder and post-traumatic stress disorder.

The researchers found daily cannabis use was associated with higher rates of CUD and “co-morbid psychiatric diagnoses” and said clinicians should screen for both.

The 2025 anonymous online survey of adults with ADHD also found differences depending on how frequently adults with ADHD used cannabis.

Daily users had higher rates of CUD and were more likely to have diagnoses including anxiety, depression, bipolar disorder and post-traumatic stress disorder.

The researchers found daily cannabis use was associated with higher rates of CUD and “co-morbid psychiatric diagnoses” and said clinicians should screen for both.

What does this mean for patients?

Current evidence does not show that cannabis will necessarily make ADHD worse.

Some adults with ADHD report improvements in symptoms such as impulsivity and mental frustration, while others report worsening inattention.

But one finding is more consistent – people with ADHD appear to be more likely to experience cannabis use disorder, while daily cannabis users with ADHD have also been found to have higher rates of CUD and other mental health diagnoses.

That does not mean cannabis caused these outcomes. Much of the research is observational, meaning it can identify relationships between cannabis use and particular outcomes but cannot prove that one caused the other.

There is also very little research looking specifically at these risks among ADHD patients prescribed cannabis-based medicines under medical supervision.

As a result, the evidence cannot yet tell us whether medical cannabis is beneficial or harmful for people with ADHD overall – or which patients may be more likely to experience benefits or risks.

Larger controlled trials are needed to examine prescribed cannabis-based medicines in people with ADHD, including their effects on core ADHD symptoms, mental health and dependence.

Find out more 

The evidence around ADHD, autism and cannabis-based medicines will be explored at the Cannabis Health Symposium in London on 26 November 2026.

The Medical cannabis and neurodiversity: exploring evidence and experience panel will examine existing research alongside patient experiences and gaps in conventional treatment.

See the session and book tickets

What does the research show?

Study	Year	Design	Participants	What it found
Cooper et al., European Neuropsychopharmacology	2017	Randomised placebo-controlled pilot trial	30 adults with ADHD	Sativex did not significantly improve the primary outcome; some secondary measures showed possible improvements, but larger trials were needed.
Ittiphakorn et al., Neuropsychopharmacology Reports	2023	Observational case series	68 ADHD patients	Improvements in anxiety, sleep and some quality-of-life measures were reported, but the study did not measure core ADHD symptoms or establish causation.
Froude et al., Journal of Psychiatric Research	2024	Meta-analysis	14 studies	People with ADHD were around three times as likely to have CUD as the general population.
Nielsen et al., Nature Mental Health	2024	Genetic study	Large genetic datasets	Identified shared genetic factors between ADHD and CUD, but did not establish causation.
Ryan et al., Journal of Attention Disorders	2025/26*	Online survey	900 adults with ADHD	Cannabis users reported mixed effects; daily users reported worsening inattention alongside improvements in some symptoms and had higher rates of CUD.