Alcohol and cannabis are two of the most widely consumed psychoactive substances in the world, if we exclude some less intoxicating ones such as caffeine and theine. Since the initial effects of these two drugs are associated with physical and psychological relaxation, it is common for many people to take them simultaneously to facilitate a synergy.

In this article we will see how the combination of alcohol and marijuana affects the brain, as well as the potential risks of this practice. In order to do so, we need to first stop and analyse the effects of each of these substances separately.

How does alcohol affect the brain?

Alcohol exerts depressive effects on the central nervous system ; roughly this means that it inhibits its activity. However, if the dose consumed is low, alcohol causes a reduction in behavioural inhibition (which many people associate with increased sociability) and feelings of relaxation and emotional release.

When the dose is high, signs such as deficits in working memory and other executive functions, problems with motor coordination – including expressive language – blurred vision and emotional disturbances, for example decreased control over anger, appear. Severe intoxication can lead to an alcoholic coma and even death .

Five phases of alcohol intoxication have been described depending on the blood concentration of this compound: the euphoric phase (characterized by impulsivity), the intoxication phase (which causes lack of coordination), the confusion phase (in which drowsiness and dysarthria appear), the stupor and coma phase and, finally, the bulbar phase or death by cardiorespiratory arrest.

Effects of cannabis use

In general marijuana produces relaxing effects in the body . However, the reactions resulting from the use of this drug can vary according to different variables, including the dose used, the characteristics of the person’s body and the variety used. The indica tends to be more interfering than the sativa.

The main active component of cannabis is cannabinoids, compounds found in some plants that activate specific receptors in the human body: the cannabinoid receptors. The most important is tetrahydrocannabinol or THC, which explains the effects of relaxation, perceptual distortion, fatigue and increased appetite .

By binding to cannabinoid receptors, THC alters the body’s levels of dopamine and noradrenaline; this causes a feeling of well-being, promotes introspection and increases sensory awareness, although it also negatively affects cognitive performance and can cause acute anxiety , even anxiety attacks.

The combination of alcohol and marijuana

Since both marijuana and alcohol intoxication decrease cognitive and behavioral performance (including notably impaired working memory), it is not surprising that by taking both substances these effects are greater than if only one is used.

In particular, research such as that of Hartman’s team (2015) suggests that, by combining these two drugs, alcohol enhances the effects of marijuana since it increases the concentration of THC in the blood, and this is the main psychoactive component of cannabis.

In contrast, according to a study by Lukas’ group (2015), using marijuana alters gastrointestinal motility; this causes alcohol to be absorbed more into the body, leading to a decrease in the effects of alcohol.

It is important to take into account that people who are physically and/or psychologically dependent on one of these substances have a high risk of developing polydrug dependence if they start to combine it with the other , since they have synergistic effects and can act as mutual substitutes.

Physiological and psychological effects of this mixture

Consuming alcohol first and then marijuana increases THC concentration because alcohol facilitates its absorption in the digestive tract. Although some people practice this combination recreationally, it can cause unpleasant physical and cognitive reactions, especially if the amount of alcohol is excessive.

In particular, many people report signs such as pallor, feelings of dizziness and weakness, nausea and vomiting . Furthermore, the mixture of these two substances increases the probability of psychological symptoms appearing, mainly anxiety (which sometimes even leads to anxiety attacks) and paranoid thoughts.

The combined use of alcohol and cannabis is one of the most common causes of road accidents worldwide. This is due to the fact that mixing both substances significantly worsens the ability to concentrate and react quickly, two very important skills in driving a vehicle.

Bibliographic references:

  • Hartman, R. L., Brown, T. L., Milavetz, G., Spurgin, A., Gorelick, D. A., Gaffney, G. & Huestis, M. A. (2015). Controlled cannabis vaporizer administration: blood and plasma cannabinoids with and without alcohol. Clinical Chemistry, 61(6): 850-69.
  • Lukas, S. E., Benedikt, R., Mendelson, J. H., Kouri, E., Sholar, M. & Amass, L. (1992). Marijuana attenuates the rise in plasma ethanol levels in human subjects. Neuropsychopharmacology, 7(1): 77-81.
  • Lukas, S. E. & Orozco, S. (2001). Ethanol increases plasma Delta(9)-tetrahydrocannabinol (THC) levels and subjective effects after marijuana smoking in human volunteers. Drug and Alcohol Dependence, 64(2): 143-9.