Neuroscience of Alcohol and Marijuana Impaired Driving

Alcohol is one of the most widely used intoxicants. The effects of driving while intoxicated
are well documented, leading to the laws and regulations behind drunk driving. Marijuana is
also a commonly abused drug, whose use is increasing with widespread
legalization/decriminalization in many US states and use of medical marijuana. Marijuana use
is linked to cognitive impairment and is likely be the cause of intoxication-induced
accidents. The effects of marijuana intoxication on driving impairments are less documented
than those of alcohol. However, most marijuana users also consume alcohol when smoking
cannabis, and preliminary data strongly suggest that driving impairment from both drugs used
together is synergistic rather than just additive.

Data are being gathered currently in regards to the risk of marijuana-impaired driving from
our NIDA-funded Neuroscience of Marijuana Impaired Driving study. Previously we had a grant
award from NIAAA that investigated alcohol-impaired driving using a similar design. The
current proposed study combines elements of both the NIDA and NIAAA studies, to assess the
cognitive and brain impairment due to the simultaneous combination of beverage alcohol and
smoked marijuana.

Our own prior NIAAA-funded grant, the Brain and Alcohol Research with College Students
(BARCS) study, along with epidemiological investigations reveal that most marijuana smokers
also consume alcohol when intoxicated. These drugs interact pharmacodynamically and change
each other's levels in the user's blood and saliva reference Marilyn study. They both have
separate, deleterious effects on driving. These effects are not additive but rather
multiplicative. A person using both substances will show more deleterious effects on driving
performance than the same individual using just one of these substances. This study will aim
to investigate the brain and behavior in the same individuals, using a similar design to the
current Neuroscience of Marijuana Impaired Driving and the prior Alcohol and Driving Grant,
that used similar techniques and measures to quantify drunk automobile driving. We
hypothesize that alcohol and marijuana use combined will lead to greater impairment in a
simulated driving task, as well as other driving-related cognitive impairments. In a
randomized, counterbalanced, double-blind study, we will dose participants with alcohol to a
legal level of 0.05% blood alcohol content, then we will administer a moderate inhaled dose
of THC marijuana or placebo marijuana, using paced inhalation that employees a vaporizer.
Participants will comprise 10 regular alcohol and marijuana consumers aged 21 to 40 years of
age; all participants must report smoking marijuana and drinking alcohol together. Of the 10,
5 will be occasional marijuana smokers and 5 frequent marijuana smokers. Following this
dosing, we will assess impairment through cognitive testing as well as a simulated driving
test through fMRI and neuropsychological tests. Samples of breath, blood and oral fluid will
also be collected at multiple time points throughout the study visits to be measured for
alcohol and THC concentration and its metabolites. This allows clarification between the
relationship of impairment, as well as subjective and objective intoxication, and levels of
THC and its metabolites in the users system.

Inclusion Criteria:

- Must have a current drivers license

- Must have used marijuana and alcohol in combination before

- Right handed

Exclusion Criteria:

- Females who are pregnant or breastfeeding

- Unable or unsafe to have an MRI

- Any serious medical or neurological disorder

- Any psychiatric disorder

- No major head traumas