Polysubstance use, the combination of two or more psychoactive substances, is common among cannabis users. This mixing is often intentional, done to enhance or alter the desired effects or to counteract an unwanted side effect. Users seek a more intense or different experience than cannabis alone provides. However, introducing a second substance can significantly and unpredictably change the physiological effects and safety profile of cannabis use. This article examines the safety implications and specific interactions that occur when cannabis is combined with other commonly co-ingested substances.
Combining Cannabis and Alcohol
The simultaneous use of cannabis and alcohol, often referred to as “cross-fading,” is the most frequently encountered combination. This practice can lead to a more intense state of intoxication than either substance alone, often resulting in severe impairment. Both compounds affect the central nervous system, and their combined action can lead to extreme impairment of cognitive function, motor skills, and judgment.
A key concern lies in a pharmacokinetic interaction where alcohol increases the absorption of Delta-9-tetrahydrocannabinol (THC). Studies have shown that consuming alcohol before using cannabis can result in significantly higher peak THC concentrations in the blood compared to using cannabis alone. This accelerated and intensified delivery of THC contributes to a stronger high that can trigger acute adverse effects like nausea, vomiting, dizziness, anxiety, or paranoia.
Alcohol can also mask the initial effects of cannabis, leading users to misjudge their level of intoxication and potentially overconsume one or both substances. This combined use increases the risk of engaging in risky behaviors, such as impaired driving, and elevates the possibility of alcohol poisoning due to higher overall consumption. The compounded impairment of reflexes and decision-making abilities significantly increases the likelihood of accidents or injury.
Interactions with Central Nervous System Depressants
Mixing cannabis with Central Nervous System (CNS) depressants presents a significantly higher degree of danger due to the risk of additive or synergistic effects. CNS depressants include prescription medications such as opioids, benzodiazepines, sleeping pills, and certain muscle relaxers. These substances slow down normal brain function, leading to effects like drowsiness, reduced anxiety, and muscle relaxation.
When cannabis is combined with these depressants, a pharmacodynamic interaction occurs, meaning the drugs’ effects on the body are compounded. This combination can lead to dangerously increased sedation, extreme impairment of coordination, and profound cognitive slowing. The most serious outcome is an increased risk of respiratory depression, a condition where breathing becomes dangerously slow and shallow.
While cannabis alone is not associated with fatal respiratory depression, combining it with other CNS depressants, particularly opioids or benzodiazepines, significantly elevates this risk. The combined effect on the central nervous system can be unpredictable, increasing the likelihood of respiratory failure, coma, or accidental injury because of extreme sedation and loss of consciousness.
The Effects of Mixing Cannabis and Nicotine
The co-use of cannabis and nicotine, often by smoking them together in a “spliff” or “blunt,” introduces a different set of risks that primarily affect the cardiovascular system and the potential for dependence. Both nicotine and THC are known to increase heart rate and blood pressure acutely. Combining them places a greater, immediate strain on the heart, as the stimulant effects of nicotine compound the tachycardia (increased heart rate) and hypertension caused by THC.
Nicotine is a well-established addictive substance, and its co-administration with cannabis can modify the addiction profile for both. Research suggests that combining the two substances may increase the risk of developing dependence on both nicotine and cannabis, making cessation more difficult. Some users report that nicotine enhances the desired psychoactive effects of cannabis, which may unintentionally reinforce the habit of co-use and increase overall exposure to both substances.
Beyond the addiction risk, smoking cannabis with tobacco introduces the health risks associated with tobacco use, including exposure to numerous toxins and carcinogens. Co-use is associated with worse symptoms of cannabis dependence, poorer cessation outcomes, and greater respiratory symptoms compared to using either substance alone. Cannabis use is associated with an increased risk of heart attack and stroke, a risk that is compounded when combined with nicotine.
General Principles for Risk Minimization
Individuals choosing to combine cannabis with any other substance should employ harm reduction strategies to minimize potential dangers. It is prudent to begin with a very small amount of both substances, often less than half of what would be consumed alone, to gauge the combined effect. Staggering consumption, such as delaying the use of the second substance, can help a person better understand and manage the effects of the first drug before introducing the second.
Ensuring a safe, familiar environment with trusted individuals present can mitigate the risks associated with impaired judgment, anxiety, or accidental injury. Understanding individual tolerance and response is also paramount, as the effects of combined substances are highly unpredictable and can differ significantly from person to person. Avoiding the combination of cannabis with any prescription CNS depressant is the safest measure due to the profound risk of respiratory depression.