New challenges such as rate of infectious diseases, drug-induced deaths and prison population push governments to adopt new drug policy around the globe. However, intervention to any substance use may also affect other types of drug-related problems, which is defined as substitution effect.
Predicting the set of the social impact of the policy is difficult to exercise because numerous factors and assumptions need to be considered. The outcomes rely on characteristics of the user population, consumption practices, potency, structure of the legal system, level of enforcement, and so on. Moreover, even the relationship between cannabis and other substances, such as alcohol, could vary under a legal regime, as income effects and legal risks could shift market demand in unpredictable ways.
Frameworks of substitution
I will give brief information about the interaction between alcohol and cannabis in this text. The association has emerged from three different perspectives; substitution, complementary and independent relationship. It is considered that cannabis regulation may alter alcohol use as in four different ways.
(a) economic shifts affecting end-user costs
(b) shifts in policy which affect availability
(c) legal shifts that affect criminal risk and associated repercussions or
(d) psychoactive/pharmacological substation.
It is expected that the policies designed to limit alcohol use have an unintended consequence of increasing cannabis use or vice versa.
Arguments of substitution effect
It is claimed that cannabis and low-dose alcohol use share neuro-pharmacologic effects of reward and sedation that could lead to substitutional effect, particularly among occasional, low-consumption users. However, people substitute drugs not only based on desired effects but also on the expected costs including price, health, legal and social consequences. For instance, people may use cannabis instead of alcohol to achieve similar intoxication effect at a lower price if costs of cannabis decrease while those of alcohol do not.
Some studies have found a substitution effect between cannabis and alcohol. Among treatment patients, reported cannabis substitution for alcohol varies from 41% to 53% in US and Canada samples. Patients at treatment reported that they substituted cannabis for alcohol, illicit drugs and prescription drugs. The reasons of substitution include (a) fewer side-effects from cannabis use compared to alcohol, illicit or prescription drugs, (b) less withdrawal from cannabis, and (c) better symptom management from cannabis.
Besides, minimum drinking age limits in the USA has a negative impact on cannabis use. A sharp decrease in cannabis use was monitored at the age of 21, while alcohol consumption increases. A similar study also shows that there is a 10% increase in the probability of drinking and an 8% increase in the probability of binge drinking among young adults at the age of 21. Moreover, it is also observed that the substitution effect between alcohol and marijuana is stronger for women than for men.
Arguments of complementary effect
On the other hand, it is also argued that liberalization of cannabis policy would lead to an increase in cannabis use, as well as an increase in alcohol use. There is support to this approach as some pharmacological studies show that the plasma tetrahydrocannabinol (THC) levels increase if alcohol is consumed simultaneously. If the value of cannabis, such as feeling higher, is enhanced by the consumption of other substances or vice versa, it is regarded as complementary. Pleasurable effects of cannabis may lead individuals to combine the use of both substances within a fixed, limited period, particularly among regular users. Moreover, the effects of cannabis use such as impaired judgment and decision making may lead to greater alcohol use than intended.
Some population-based studies support the complementary argument that there was an increase in both last month cannabis use and alcohol use in states allowing medical cannabis dispensaries in the USA.
Arguments of independent relationship
Finally, if the presence or absence of any substance is not altered by the use of others, this may refer to an independent relationship. Literature suggests contradicting results and it provides substantial evidence for both substitutes and complements, which may also indicate an independent relationship.
It is also important to keep in mind that the effects vary by context such as age and the cannabis policy. For instance, medical cannabis use increased the frequency of binge drinking by 6-9 percent among those aged 21 or above but it did not affect drinking behavior among 12-20 years olds in the USA.
A contradictory argument also suggests that among 8th graders, the prevalence of marijuana use, binge drinking, cigarette use, non-medical use of opioids, amphetamines and tranquilizers, and any non-marijuana illicit drug use decreased after medical cannabis use was legalized. Moreover, when the trend was analyzed in a more liberal cannabis policy context, evidence shows that 8 grade students in the Washington State were more likely to use cannabis after the cannabis legalization and they were less likely to use alcohol (12.4% vs 8.3%).
Conclusion of the substitution
Substitution exists not only between cannabis and alcohol, but also between other drugs. Nowadays, drug users constantly adjust their behaviors accordingly to the current status of drugs based on their price, availability, legal consequences, group and personal preferences. However, substitution of alcohol and cannabis is better-known but the science still evaluate the validity of the relationship. More research is needed to understand contextual factors.
Cerdá, M., Sarvet, A. L., Wall, M., Feng, T., Keyes, K. M., Galea, S., & Hasin, D. S. (2018). Medical marijuana laws and adolescent use of marijuana and other substances: Alcohol, cigarettes, prescription drugs, and other illicit drugs. Drug and Alcohol Dependence, 183, 62-68
Guttmannova, K., Lee, C. M., Kilmer, J. R., Fleming, C. B., Rhew, I. C., Kosterman, R., & Larimer, M. E. (2016). Impacts of changing marijuana policies on alcohol use in the united states. Alcoholism: Clinical and Experimental Research, 40(1), 33-46.
Lucas, P., Reiman, A., Earleywine, M., McGowan, S. K., Oleson, M., Coward, M. P., & Thomas, B. (2013). Cannabis as a substitute for alcohol and other drugs: A dispensary-based survey of substitution effect in canadian medical cannabis patients. Addiction Research & Theory, 21(5), 435-442.