Cannabis and Alcohol: Risks of Mixed Consumption
Cannabis and alcohol are the most commonly combined psychoactive substances worldwide. Many people assume that the combination simply results in “more of both” — the reality is more complicated and potentially more dangerous than the individual effects suggest. What happens in the body when they are consumed together, what “Greening Out” means, and why road traffic deserves special attention.
How alcohol changes the effects of THC
Alcohol and cannabis influence each other on a pharmacological level. The key effect: alcohol increases the blood plasma concentration of THC.
Studies show (among others, Lukas & Orozco, 2001): Those who drink alcohol before consuming cannabis have significantly higher THC blood levels than when consuming cannabis alone — at the same cannabis dose. The mechanism: alcohol increases blood flow to the stomach lining, thereby increasing the absorption of THC (especially with oral intake). With inhalation, alcohol enhances vasodilation in the airways, which increases lung absorption.
This means practically: a moderate cannabis dose that would be well tolerated on its own can lead to significantly more intense — and unpleasant — effects after alcohol.
What is “Greening Out”?
Greening Out (also known as “Whitey” in the British English-speaking world) refers to an acute reaction to cannabis overdose, often triggered by combined use with alcohol. Symptoms:
- Severe nausea and vomiting
- Pale, greenish-pale skin color (hence the name)
- Cold sweat, heart palpitations
- Extreme dizziness, disorientation
- Feeling of fainting or “I’m dying” (very anxiety-inducing, but generally not life-threatening)
- Panic attacks
Greening Out is not life-threatening — but very unpleasant and alarming for those affected. What helps:
- Lying down (a flat position prevents fainting)
- Fresh air
- Drink cold water if possible
- Calm environment, presence of a calming person
- No further consumption — wait until the effects subside
In case of unconsciousness or seizures: call emergency services at 112.
Order: “Beer before grass…” — what’s the truth?
The English idiom “Beer before grass, you’re on your ass; grass before beer, you’re in the clear” has a certain pharmacological basis:
- Alcohol first, then cannabis: Alcohol increases THC levels → higher risk of Greening Out and intense reactions
- Cannabis first, then alcohol: Less interaction with THC absorption, but alcohol can still enhance the effects and further impair judgment
Both sequences carry risks — the folk wisdom only describes which combination more frequently leads to Greening Out. It is not a valid safety rule.
Combined use and road traffic: double danger
The KCanG explicitly regulates: anyone who combines cannabis and alcohol and drives a car is legally at risk — regardless of the THC limit of 3.5 ng/ml.
According to § 24a StVG Abs. 1 and 1a, the combination (cannabis + alcohol, even below the individual limits) is considered punishable. This means:
- Already from 0.5 promille alcohol + any THC detection: administrative offense with significantly increased fine
- From 1.1 promille + THC detection: criminal offense
- Consequences: higher fines, driving ban, mandatory MPU, possible revocation of the driver’s license
Impairment due to combined use is empirically proven and greater than the sum of the individual effects — impaired reaction time, restricted judgment, reduced lane-keeping ability.
Additional risks: cardiovascular system, psychosis, memory
Alongside the acute danger, there are medium-term risks:
- Cardiovascular system: Both substances affect heart rate and blood pressure — combined use increases the risk of tachycardia and arrhythmias in at-risk individuals
- Psychotic risk: Alcohol and cannabis synergistically increase the risk of psychosis in vulnerable individuals more than either substance alone
- Memory formation: Combined use impairs memory formation (long-term potentiation in the hippocampus) more than the individual substances — the risk of blackouts increases
- Tolerance development: Those who regularly combine the two develop cross-tolerance — requiring more of both for the same effect
For medical patients: interaction with alcohol
Patients who use cannabis by prescription should reduce alcohol consumption during therapy:
- Alcohol enhances the sedative side effects of THC (especially in patients with sleep and pain issues)
- The enhanced THC absorption caused by alcohol leads to uncontrollable dosage adjustments
- Liver enzymes that break down THC (CYP3A4) are influenced by alcohol — slower breakdown is possible
Those who want to understand how cannabis works in the body: Cannabis effects and the endocannabinoid system. Regarding the driver’s license and the THC limit: Cannabis and the driver’s license. Regarding interactions with medications: Cannabis interactions.
Mixed consumption further increases cardiovascular risk: Cannabis and Heart Health: Tachycardia, Blood Pressure, and Risks — why alcohol + THC doubly burdens the cardiovascular system.
Alongside alcohol, caffeine is a common cannabis combination: Cannabis and Caffeine: What Happens with the Combination? — pharmacologically less risky than alcohol, but with its own interactions.
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