Cannabis & alcohol: combination, risks & crossfade

Cannabis and alcohol: two substances, one complex interaction

Cannabis and alcohol are the psychoactive substances most frequently consumed together worldwide. In countries with cannabis legalization, the use of combinations continues to rise. The combination is not a neutral addition – through pharmacological interactions, it produces effects that go beyond the sum of the individual substances. This makes the combination riskier than many users expect.

Pharmacological interactions

Alcohol increases THC absorption: Alcohol (even in low doses) increases the gastrointestinal absorption of orally ingested THC. Lukas et al. 1992 (Clin Pharmacol Ther): Alcohol significantly increases maximum THC plasma concentration (Cmax). With joints (inhaled) the effect is smaller, but also measurable – presumably due to vasodilation and increased pulmonary absorption.

Combined CNS effect: Both substances dampen the CNS via different mechanisms:
– Alcohol: GABA-A enhancement + NMDA inhibition
– THC: CB1 activation + dopamine modulation

Combined, they produce a synergistic CNS depressant effect that impairs reaction time, coordination and judgment more than either substance alone.

Crossfade: The phenomenon explained

Crossfade (or greening out) refers to the intense discomfort of combining cannabis and alcohol:
– Dizziness, nausea, severe vomiting
– Sweating, pallor
– Palpitations, feeling of panic
– In severe cases: Fainting

Mechanism: Alcohol increases THC plasma concentrations (Lukas 1992). At the same time, alcohol inhibits the vestibulocerebellar system (balance) while THC has a tachycardiogenic effect. The combination overloads the homeostatic regulatory systems.

Risk factor: alcohol first, then cannabis = highest crossfade risk. Cannabis first, then alcohol = lower risk (alcohol absorption possibly slower).

Study situation: Cognitive and traffic risks

Road safety: particularly critical

The traffic risks of the combination are particularly well documented. Ramaekers 2006 and Downey 2013 (both RCTs with driving simulator) show consistently:
– Combination of cannabis + alcohol = significantly worse driving performance than either substance alone
– Even small amounts of alcohol (0.3-0.5 per mille) significantly increase cannabis driving impairment
– The new German THC limit (3.5 ng/ml) does not apply in combination with alcohol → criminal consequences

Long-term risks with chronic combination consumption

– Cognition: Chronic combination associated with greater cognitive deficits than either substance alone (Lisdahl 2014)
– Risk of addiction: combination use increases the development of both substance addictions
– Liver: alcohol is hepatotoxic; cannabis can modulate alcohol-induced liver damage with simultaneous alcohol consumption (ECS modulator effect – bidirectional)

FAQ: Cannabis and alcohol

Summary

Cannabis and alcohol combined is pharmacologically synergistic – alcohol increases THC absorption and both additively depress the CNS. Driving risk significantly higher with combination than with single substances (RCT data). Crossfade (especially alcohol before cannabis) is a real safety risk. Road traffic: combination = §315c StGB. Long-term: greater cognitive impairment and increased risk of addiction. Cannabis and driving license and cannabis dependence for related risk issues.