CBD and focus: what the trials actually measured

For foods, the rule comes from EU Regulation No 1924/2006: a health claim is prohibited unless it has been authorised and entered on the official lists, and no claim for CBD has been. In France the question stops earlier, because CBD foods and supplements are not authorised at all, as explained in our piece on the EFSA reference dose.

Flowers, resins or oils sold for non-food use are limited by the Public Health Code. Its article L5111-1 defines as a medicine any product "presented as having curative or preventive properties with regard to human diseases". MILDECA, the government body coordinating drug policy, is explicit: CBD products may not, "on pain of criminal penalties, claim therapeutic properties". A promised effect on an attention disorder comes within that scope.

Few studies have looked at CBD and cognitive functions (attention, memory, reasoning), and those that exist are small. Two double-blind, placebo-controlled trials provide precise measurements.

At University College London, Michael Bloomfield and colleagues gave 600 mg of CBD or a placebo to 15 healthy adults in two separate sessions. Three hours after intake, MRI showed increased blood flow in the hippocampus, a brain region linked to memory. Scores on working memory and prose recall tests were the same under CBD and placebo. More blood flow did not translate into better results.

At Maastricht University, Thomas Arkell and colleagues had 26 adults, occasional cannabis users, drive 100 km on public roads. Before each session they vaporised THC-dominant cannabis, CBD-dominant cannabis, an equal mix or a placebo, at 13.75 mg per cannabinoid. The main outcome was lane weaving, expressed as the standard deviation of the car's lateral position.

From 40 to 100 minutes after intake, CBD-dominant cannabis matched placebo, at 18.21 cm against 18.28 cm. THC added 2.33 cm and the THC and CBD mix 2.83 cm. By the team's calibration, a blood alcohol level of 0.5 g/l adds 2.4 cm. Adding CBD did not dampen the effect of THC. Four hours later, every condition was back level with placebo. The authors note that the doses tested may not match common use.

Neither trial found CBD improving attention; at these doses and on these tasks, they found no measurable effect. The 600 mg dose is also 300 times the EFSA's provisional reference of 2 mg per day for 70 kg. The few trials on attention deficit disorder are reviewed in our article on CBD and ADHD.

The Maastricht trial also speaks to a frequent question: does THC help you focus? On the road, for an hour and a half after intake, it impaired lane keeping as much as a blood alcohol level of 0.5 g/l. THC is a narcotic in France; our article on the differences between THC and CBD compares the two molecules.

A compliant CBD product may contain up to 0.30% Δ⁹-THC. MILDECA points out that driving after using narcotics is banned "regardless of the dose absorbed". On 21 June 2023, France's Court of Cassation ruled that the legal status of the product consumed is irrelevant to this offence. Detection windows are detailed in our guide to saliva drug testing, and what an employer may check is covered in our article on saliva tests at work.

The effect of sleep has been measured, and it is large. In 2003, Hans Van Dongen and colleagues followed 48 adults in a laboratory. Some slept 8, 6 or 4 hours a night for 14 days; others stayed awake three nights in a row. At 6 hours or less, cognitive deficits reached up to the equivalent of two sleepless nights. Yet their sense of sleepiness hardly rose after the first days, so participants underestimated their own loss of performance. What research says, and does not say, about CBD here is reviewed in our article on CBD and sleep.

Caffeine has been studied more than any other substance in this field. According to the EFSA, in moderate doses it increases alertness and reduces sleepiness. The agency sees no safety concern for a healthy adult up to 200 mg in a single dose and 400 mg a day. It adds that 100 mg can affect how long some adults sleep, especially when taken close to bedtime.

Check three things. First, what the product actually contains. In June 2025, ANSES, the French food and health safety agency, reported several hundred poisonings since 2024 linked to products sold as CBD that held THC above 0.3% or synthetic cannabinoids. It cites a 2023 study in which eight products out of ten did not match their stated CBD content. How to read an analysis is explained on our laboratory page.

Second, traces of THC, which a full-spectrum product contains and an isolate does not. If you drive or your job involves testing, our comparison of full spectrum and isolate will help you choose. Third, interactions with medicines through liver enzymes, explained in our article on the grapefruit effect. Drowsiness also appears among the reported side effects listed in CBD side effects.