CBD and focus: what the trials actually measured

EU Regulation No 1924/2006 sets the rule for foods: a health claim is prohibited unless it has been authorised and entered on the official lists. None has been for CBD. In France the question is settled earlier anyway: CBD foods and supplements are not authorised, as our piece on the EFSA reference dose explains.

For other products, flowers, resins or oils sold for non-food use, the limit comes from 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 that coordinates drug policy, puts it plainly: CBD products may not, "on pain of criminal penalties, claim therapeutic properties". Promising an effect on an attention disorder falls within that scope.

Studies of CBD and cognitive functions, meaning attention, memory or reasoning, are rare and small. Two of them, double-blind and placebo-controlled, give 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 higher blood flow in the hippocampus, a brain region linked to memory. Working memory and prose recall tests, however, did not differ between CBD and placebo. Higher blood flow is therefore not a better result.

At Maastricht University, Thomas Arkell and colleagues had 26 adults, occasional cannabis users, drive 100 km on public roads. In separate sessions, each had vaporised THC-dominant cannabis, CBD-dominant cannabis, an equal mix or a placebo, at 13.75 mg per cannabinoid. The main measure was how much the car weaved in its lane, measured as the standard deviation of its lateral position.

Between 40 and 100 minutes after intake, CBD-dominant cannabis gave the same result as placebo: 18.21 cm against 18.28 cm. THC added 2.33 cm, and the THC and CBD mix 2.83 cm. For comparison, the team had calibrated that a blood alcohol level of 0.5 g/l adds 2.4 cm. CBD therefore did not dampen the effect of THC. Four hours later, no condition differed from placebo any more. The authors point out that the doses tested may not reflect common use.

Neither trial shows an attention gain with CBD. They show, at these doses and for these tasks, no measurable effect. The 600 mg dose is also 300 times the EFSA's provisional reference of 2 mg per day for 70 kg. For attention deficit disorder, our article on CBD and ADHD reviews the few trials.

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

A compliant CBD product can contain up to 0.30% Δ⁹-THC. MILDECA reminds readers that driving after using narcotics is banned "regardless of the dose absorbed". France's Court of Cassation ruled on 21 June 2023 that the legality of the product consumed makes no difference to this offence. Our guide to saliva drug testing details the detection windows, and our article on saliva tests at work covers what an employer may check.

Sleep has a measured effect, and a large one. 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 were kept awake for three nights in a row. At 6 hours or less, cognitive deficits reached up to the equivalent of two sleepless nights. Their feeling of sleepiness, however, barely increased after the first days: participants misjudged their own loss of performance. Our article on CBD and sleep looks at what research does and does not say about CBD in this area.

Caffeine is the best-studied substance in this field. The EFSA states that in moderate doses it increases alertness and reduces sleepiness. For a healthy adult, the agency sees no safety concern up to 200 mg in a single dose and 400 mg a day. It also notes that 100 mg can affect sleep duration in some adults, especially close to bedtime.

Three points deserve attention. The first is what the product really 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 contained THC above 0.3% or synthetic cannabinoids. The agency cites a 2023 study in which eight products out of ten did not have the stated CBD content. Our laboratory page explains how to read an analysis.

The second concerns traces of THC. A full-spectrum product contains them, an isolate does not: our comparison of full spectrum and isolate helps you choose if you drive or if your job involves testing. The third is interaction with medicines, through liver enzymes: our article on the grapefruit effect explains it. Drowsiness is also among the reported side effects, see CBD side effects.