The answer to that question lies in how you answer it. Anyone’s tendency toward substance dependency or abuse is governed at least 50% by genetics, and 50% (or less) by psychological, social and environmental factors. [6, 16, 25, 29, 30, 32, 35, 38, 42]
One person can be satisfied with a single drink; another compulsively rushes to get blackout-wasted after – and because of – having a single drink. One person can have a slice of cake and be content; another eats a slice of cake and is triggered to binge feverishly and consume a week’s worth of calories in under an hour.
Why? At the risk of oversimplifying the answer to that, I’ll just say that each of us has a different blend of biological and psychological factors that determines our substance dependency/abuse potential. Someone who has a parent with a drug/alcohol addiction, for instance, is 8 times more likely to develop an addiction. And yet, even if you’re not genetically condemned to addiction like that, you can still physically rewire your brain on your own and end up that way. 
So, let me rephrase the original question: Which substance – marijuana, alcohol, caffeine, sugar or nicotine – is most addictive to you? Well, take a look at the risk factors I’ve discovered for each and decide for yourself. And if you’d like a more thorough answer, consult the references cited in brackets and hyperlinked in the endnotes.
A Note on the Connection Between Addiction and Marijuana, Alcohol, Caffeine, Sugar and Nicotine
Each substance examined in this article is connected to addiction by virtue of its role in releasing the feel-good chemical dopamine in your brain. You might sneer at the suggestion that sugar can be addictive when it’s not landing people in rehab or prison, but it’s a scientifically proven addictive substance. In fact, it’s actually more addictive than something you’d have no objection to hearing described as “addictive”: cocaine. [56, 60] How? Dopamine.
Here’s how someone far smarter than I am explains the chemistry of addiction:
“When an individual engages in a behavior that the brain perceives as beneficial to survival (due to thousands of years of evolution and basic instinct), it produces a chemical signal called dopamine. Dopamine is the chemical that causes feelings of pleasure and happiness. The brain uses it as a reward system to reinforce certain behaviors. For example, the brain perceives sex as important for procreation. So it produces high levels of dopamine during and after sex in order to reinforce that it’s a good, useful action. And to encourage the individual to engage in that same behavior again. In comparison, drugs cause the brain to flood with dopamine and trick it into believing that drugs are necessary and important for human survival. Over time, the brain loses its ability to produce its own dopamine and depends on substances to create it. This is how addiction happens.” 
So, anything that tinkers with your brain’s pleasure hormone has the potential for abuse and dependence. Don’t discount that fact. Also, anytime something is tinkering with your brain before it’s fully developed (age 25 ), that tinkering is going to have a permanent effect on your brain. That’s why teens are exponentially more vulnerable to becoming addicted than adults are.
“Addiction” is defined differently within each field of study, and even among institutions within the same field. The best definition I found while doing research was in the journal article “Considering the Definition of Addiction,” which states: “Elements of addiction … include: (a) engagement in the behavior to achieve appetitive effects, (b) preoccupation with the behavior, (c) temporary satiation, (d) loss of control, and (e) suffering negative consequences.”  By extension, “addictive” refers to an increased probability of experiencing those elements.
Marijuana (Cannabis Sativa or Indica)
You’re more prone to marijuana addiction if:
- The marijuana you consume has a high THC level. [10, 16]
- You’re under 18. [10, 11, 13, 14, 16, 19, 20]
- You’re addicted to another substance (e.g., nicotine). [12, 16]
- You have a mental health condition (e.g., anxiety, post-traumatic stress disorder, schizophrenia). 
- You have a decreased response to dopamine. 
- You consume it every day. 
You might be addicted to marijuana if:
- You experience withdrawal symptoms (irritability, mood and sleep difficulties, decreased appetite, cravings, restlessness) when not consuming it. [11, 14, 16, 17, 19, 20, 23, 73]
- You can’t stop consuming it despite experiencing bad things from it. [11, 13, 14, 16, 19, 23, 24, 73]
- You always end up consuming more than you planned. [17, 73]
- You couldn’t stop consuming it if you wanted or needed to. [16, 17, 23, 73]
- You’ve developed a tolerance to it and need more of it to get the same feeling. [19, 24]
- You give up social, occupational and/or recreational activities to consume it. [19, 24, 73]
- You lie about how much you consume to avoid being accused of addiction. 
Other findings about marijuana:
- Today’s (2019) marijuana has 3 times the concentration of THC than the marijuana of 25 years ago did. [10, 16, 22]
- People who begin using marijuana before the age of 18 are 4 to 7 times more likely to develop a marijuana addiction. 
- In 2014, states that had legalized medical marijuana reported a 25% drop in deaths resulting from an overdose of pain medication, attributed to replacing dangerous pain medicines with marijuana. 
You’re more prone to alcohol addiction if:
- You started drinking regularly as a teenager. [21, 27, 28, 32, 35, 37]
- You have a parent or other close relative who is/was addicted to alcohol. [27-30, 35, 36]
- You’re depressed or have another mental health disorder (e.g., anxiety, schizophrenia, bipolar disorder). [27, 28, 30, 32, 35]
- You have a history of sexual, emotional or other trauma. [27, 30, 32]
- You’ve had bariatric surgery for weight loss. [27, 30]
- You have a close friend or partner who drinks often. [27, 28, 30]
- You were raised by (or spent a lot of time around as a child) someone addicted to alcohol. [28, 30]
- You’re in a career path with high levels of stress due to long hours and strenuous tasks. 
- You’re an impulsive person. 
- You have low self-esteem and a strong need for others’ approval. [32, 35]
- You grew up without a father figure. 
You might be addicted to alcohol if:
- You binge drink on a regular basis. [22, 27, 28, 32]
- You can’t stop consuming it despite experiencing bad things from it. [21, 27, 32, 73]
- You couldn’t stop consuming it if you wanted or needed to. [21, 27, 73]
- You often end up consuming more than you planned. [21, 28, 32, 73]
- You give up social, occupational and/or recreational activities to consume it. [21, 27, 31-33, 73]
- You lie about how much you drink and/or hide while drinking. [31, 73]
- You experience withdrawal symptoms (nausea, sweating, rapid heartbeat, hand tremors, problems sleeping, shaking) when not consuming it. [27, 32, 35, 73]
- You’ve developed a tolerance to it and need more of it to get the same feeling. [21, 27, 31, 32]
- You spend an extreme amount of time trying to get, drink and/or recover from alcohol. [21, 27, 32]
- You’re preoccupied with drinking and think about it all the time. [27, 28, 32]
- You want to drink less but fail when trying. [27, 32]
- You feel a strong craving or urge to drink alcohol. [21, 27, 28]
- You drink alcohol when you know it’s not safe (e.g., before driving) or appropriate (e.g., at work). [27, 31]
- Friends, loved ones and/or coworkers have expressed a concern about your drinking. 
- You can’t stay sober for an extended period of time. 
- You don’t get hungover. 
- You avoid going places where there won’t be any alcohol. 
- You’ve changed your social circle to consist largely of other drinkers. 
- You need alcohol to function in everyday life and/or feel normal. [31, 35]
- You miss important functions (school, work, etc.) because of your drinking. 
- You drink to the point of blacking out. [27, 32]
Other findings about alcohol:
- Almost half of those who begin drinking at age 14 or younger become alcoholics. 
- Worldwide, alcohol is the cause of 1 in every 20 deaths. 
- Alcohol dependence is associated with 51 genes that make family members much more prone to developing drinking problems. 
- An estimated two-thirds of the American population consumes alcohol, but half of all the alcohol consumed in the country is consumed by only 10% of drinkers. 
You’re more prone to caffeine addiction if:
- You have a co-occurring mental health disorder (e.g., insomnia, eating disorder). 
- You consume caffeine in coffee, tea, soda, energy drinks or something else regularly (daily) for a long time. [39, 44, 49]
- You generally lack energy and motivation, or you’re depressed. 
- You’re a workaholic. 
- You’re a chocoholic. 
You might be addicted to caffeine if:
- You regularly drink a lot (more than four cups) of coffee per day. [39, 40, 48, 49]
- You can’t stop consuming it despite experiencing bad things (sleep disruption, migraines and other headaches, irritability, quickened heartbeat, muscle tremors, nervousness, nausea) from it. [39, 42, 43, 46, 50, 51, 73]
- You couldn’t stop consuming it if you wanted or needed to. 
- You always end up consuming more than you planned. [39, 73]
- You give up social, occupational and/or recreational activities to consume it. [42, 73]
- You experience withdrawal symptoms (headaches, irritability, fatigue, anxiety, difficulty concentrating, depressed mood, tremors, low energy, mental fogginess) when not consuming it. [39, 42, 44-46, 49-51, 73]
- You’ve developed a tolerance to it and need more of it to get the same feeling. [39, 42, 48, 49]
- You become highly distressed when you want caffeine and can’t get it. [39, 49]
- Your daily life is highly disrupted when you can’t get caffeine. [39, 49]
- You want to consume less of it but fail when trying. [39, 42, 50, 51]
- You spend a lot of time obtaining, consuming and/or recovering from caffeine. 
- You feel a strong craving or urge to consume caffeine. [39, 42]
- You can’t feel normal or function normally until you’ve had some caffeine. [39, 44, 45, 49, 51]
- You can’t have fewer than two cups of coffee per day. 
- You can’t control how much you consume. 
- You can’t relax at bedtime even when you feel fatigued. 
- You avoid emotional difficulties by consuming caffeine. 
- You need caffeine to stay awake and rely on it to wake up. [48, 50]
- You’re convinced that caffeine is necessary for success at work or school. 
Other findings about caffeine:
- Caffeine impersonates the molecule in your brain that indicates sleepiness (adenosine) and blocks that molecule’s cell receptors, preventing your brain from discovering that you’re sleepy. In response, your brain releases natural stimulants like dopamine. [39, 40, 43, 44, 48]
- High doses of caffeine (more than 750 milligrams every day) can produce complete tolerance, stripping caffeine of its effect on you. 
- One ounce of milk chocolate contains 1 to 15 milligrams of caffeine, and 1 ounce of dark chocolate has 5 to 35 milligrams of caffeine. 
- Coffee activates a system in our brains that secretes marijuana-like chemicals that control feelings of hunger and levels of happiness and euphoria. 
You’re more prone to sugar addiction if:
- You frequently experience low moods, anxiety and stress. 
- You suffer from constant tiredness. 
- You have a parent who is addicted to alcohol. 
- You are in the early stages of recovery from drug or alcohol addiction. 
You might be addicted to sugar if:
- You crave sugar to balance irritability, emotional lows or other conditions. 
- You crave sugar after stressful or irritating life experiences. 
- You can’t stop consuming it despite experiencing bad things (weight gain, headaches, hormone imbalances, diabetic complications) from it. [53, 73]
- You couldn’t stop consuming it if you wanted or needed to. 
- You give up social, occupational and/or recreational activities to consume it. 
- You experience withdrawal symptoms (irritability, fogginess, moodiness, low energy) when not consuming it. [52, 57, 73]
- You experience a loss of self-control while consuming it. [52, 55]
- You find yourself consuming more and more it. 
- You eat more foods with sugar than you want to. 
- You eat sugary foods to the point of feeling ill or unsettled. 
- You have cravings for simple carbohydrates or simple sugars. 
Other findings about sugar:
- Sugar can be even more addictive than cocaine, activating more neurons in the brain’s pleasure center than cocaine does. [56, 60]
- Dopamine receptors in the brain light up when we consume sugar in a way similar to how the receptors light up in the brain of someone who abuses alcohol. [52, 62]
- Excessive sugar impairs cognitive skills and self-control. [55, 56, 61]
- High sugar consumption leads to memory difficulties. [55, 56, 61]
- Sugar is hidden in ingredients lists as words that end in “ose,” such as “fructose,” “dextrose,” “maltose” and “sucrose” (the chemical name for table sugar). 
- Repeated sugar binging can have a gateway effect and lead to an increased risk for abusing drugs. 
You’re more prone to nicotine addiction if:
- You’re in your teens now, or you started smoking or vaping in your teens. [26, 41, 66, 67, 69, 70, 72]
- You regularly abuse alcohol and/or other drugs. [26, 65, 72]
- You have a family history of smoking. [65, 69]
- Your mother or grandmother was a smoker. 
- You were raised by (or spent a lot of time around as a child) a smoker. [65, 69]
- You’re depressed or have another mental health condition. 
You might be addicted to nicotine if:
- You can’t stop consuming it despite experiencing bad things (health issues, relationship issues, etc.) from it. [26, 64, 65, 69, 72, 73]
- You experience withdrawal symptoms (irritability, craving, depression, anxiety, cognitive and attention deficits, sleep disturbances, increased appetite) when not consuming it. [15, 64, 65, 69, 71-73]
- You’ve tried to quit smoking or vaping but couldn’t. [65, 66, 69, 70, 72]
- You give up social, occupational and/or recreational activities to consume it. [65, 72, 73]
- You avoid going places where you won’t be able to smoke. [65, 72]
- You have specific craving triggers, such as finishing a meal or driving. [65, 69]
- You crave nicotine when you’re stressed. 
- You feel irritated or anxious when you can’t use tobacco. 
- You experience cravings for nicotine. 
- You go out of your way to get tobacco. 
- You need higher doses to feel the same initial effects. 
- Your body doesn’t feel normal without a cigarette. 
Other findings about nicotine:
- Of those who smoke, 80% to 90% started by the age of 18. [26, 69, 72]
- On average, smokers live 14 years fewer than nonsmokers live. [26, 70]
- The success rate for quitting smoking is 6% for the first attempt, and most smokers need multiple attempts before succeeding. 
- Nicotine levels peak within 10 seconds of inhalation, then dissipate quickly. 
- One vape manufacturer produces a “pod mod” that contains 0.7 milliliters of nicotine, which is about the same as 20 regular cigarettes. 
- By their senior year, over 25% of high schoolers are e-cigarette users. 
- Nicotine is as addictive as cocaine and heroin. 
- You can develop an addiction to nicotine within minutes. 
There’s no quantifiable approach to measuring addictiveness generically. When I set out to write this article, I was expecting to find percentages – even a 20-point spread – for each substance, and my plan was to compare them that way. But I reviewed more than 70 sources, and I learned that there’s no such thing as, “XYZ is 50% addictive.” And that’s because you can’t end the sentence there; you have to follow the declaration with a qualifier like “to children under 18.” And if anyone hands you some one-size-fits-all statistic that doesn’t account for the variables I presented in this article, call them out on their ignorance. As convenient as it would be to be able to say, “Everyone has a 50% chance of becoming addicted to XYZ,” the reality is, someone’s tendency toward any addiction is as complicated as the addiction itself.
 “Definition of Addiction,” Quality & Science, American Society of Addiction Medicine, accessed February 29, 2020. https://www.asam.org/Quality-Science/definition-of-addiction.
 “What Is Addiction?,” Addiction and Substance Use Disorders, American Psychiatric Association, accessed February 29, 2020. https://www.psychiatry.org/patients-families/addiction/what-is-addiction.
 Steve Sussman and Alan N. Sussman, “Considering the Definition of Addiction,” International Journal of Environmental Research and Public Health 8, 10 (October 2011), https://dx.doi.org/10.3390%2Fijerph8104025.
 “The Science of Drug Use and Addiction: The Basics,” National Institute on Drug Abuse, accessed February 29, 2020. https://www.drugabuse.gov/publications/media-guide/science-drug-use-addiction-basics.
 “Behavioral Addictions,” American Addiction Centers, last modified February 3, 2020. https://americanaddictioncenters.org/behavioral-addictions.
 “Addictions,” American Psychological Association, accessed February 29, 2020. https://www.apa.org/topics/addiction/.
 “What Is Addiction?,” Psychology Today, accessed February 29, 2020. https://www.psychologytoday.com/us/basics/addiction.
 “Drug Scheduling,” U.S. Drug Enforcement Administration, accessed February 29, 2020. https://www.dea.gov/drug-scheduling.
 Substance Abuse and Mental Health Services Administration, Key Substance Use and Mental Health Indicators in the United States: Results from the 2018 National Survey on Drug Use and Health (HHS Publication No. PEP19-5068, NSDUH Series H-54). Rockville, MD: Center for Behavioral Health Statistics and Quality, accessed February 29, 2020. https://www.samhsa.gov/data/sites/default/files/cbhsq-reports/NSDUHNationalFindingsReport2018/NSDUHNationalFindingsReport2018.pdf.
 “Know the Risks of Marijuana,” Substance Abuse and Mental Health Services Administration, accessed February 29, 2020. https://www.samhsa.gov/marijuana.
 “Is marijuana addictive?,” National Institute on Drug Abuse, accessed February 29, 2020. https://www.drugabuse.gov/publications/research-reports/marijuana/marijuana-addictive.
 “Is marijuana a gateway drug?,” National Institute on Drug Abuse, accessed February 29, 2020. https://www.drugabuse.gov/publications/research-reports/marijuana/marijuana-gateway-drug.
 “Some Things to Think About,” Marijuana: Facts for Teens, National Institute on Drug Abuse, accessed February 29, 2020. https://www.drugabuse.gov/publications/marijuana-facts-teens/some-things-to-think-about.
 “What is marijuana?,” DrugFacts, National Institute on Drug Abuse, accessed February 29, 2020. https://www.drugabuse.gov/publications/drugfacts/marijuana.
 “Quitting Smoking,” Centers for Disease Control and Prevention, accessed February 29, 2020. https://www.cdc.gov/tobacco/data_statistics/fact_sheets/cessation/quitting/index.htm.
 R. Sam Barclay, “Marijuana Can Be Addictive: Who Gets Hooked and Why,” Healthline Media, last modified August 2, 2019. https://www.healthline.com/health-news/marijuana-addiction-rare-but-real-072014#1.
 “10 Signs of Marijuana Addiction,” The Canyon, accessed February 29, 2020. https://thecanyonmalibu.com/blog/10-signs-of-marijuana-addiction/.
 “What are hallucinogens?,” DrugFacts, National Institute on Drug Abuse, accessed February 29, 2020. https://www.drugabuse.gov/publications/drugfacts/hallucinogens.
 Office of National Drug Control Policy, Marijuana Myths and Facts: The Truth Behind 10 Popular Misperceptions, National Criminal Justice Reference Service, accessed 29 February, 2020. https://www.ncjrs.gov/ondcppubs/publications/pdf/marijuana_myths_facts.pdf.
 “What Is Marijuana?,” Hazelden Betty Ford Foundation, accessed February 29, 2020. https://www.hazeldenbettyford.org/addiction/types-of-addiction/marijuana.
 “Understanding Alcohol,” Alcohol Addiction and Abuse, Addiction Center, accessed February 29, 2020. https://www.addictioncenter.com/alcohol/.
 “Statistics on Addiction in America,” Addiction Statistics, Addiction Center, accessed February 29, 2020. https://www.addictioncenter.com/addiction/addiction-statistics/.
 “Understanding Marijuana,” Marijuana Addiction and Abuse, Addiction Center, accessed February 29, 2020. https://www.addictioncenter.com/drugs/marijuana/.
 “Signs of Marijuana Abuse,” Marijuana Symptoms and Warning Signs, Addiction Center, accessed February 29, 2020. https://www.addictioncenter.com/drugs/marijuana/symptoms-signs/.
 “What Is Addiction?,” Addiction, Addiction Center, accessed February 29, 2020. https://www.addictioncenter.com/addiction/.
 “Understanding Nicotine,” Nicotine Addiction and Abuse, Addiction Center, accessed February 29, 2020. https://www.addictioncenter.com/nicotine/.
 “Alcohol use disorder,” Mayo Clinic, accessed February 29, 2020. https://www.mayoclinic.org/diseases-conditions/alcohol-use-disorder/symptoms-causes/syc-20369243?mc_id=us&utm_source=newsnetwork&utm_medium=l&utm_content=content&utm_campaign=mayoclinic&geo=national&placementsite=enterprise&cauid=100721&_ga=2.138881907.1702462402.1581899007-1248366573.1581899007.
 “Alcoholism Causes and Risk Factors,” Alcohol Rehab Guide, accessed February 29, 2020. https://www.alcoholrehabguide.org/alcohol/causes/.
 “How Easy Is it to Get Addicted to Alcohol,” summitBHC, last modified November 5, 2015. https://summitbhc.com/how-easy-is-it-to-get-addicted-to-alcohol/.
 “What Makes Alcohol Addictive?,” The Recovery Village, accessed February 29, 2020. https://www.therecoveryvillage.com/alcohol-abuse/faq/makes-alcohol-addictive/#gref.
 “Alcohol Addiction,” Healthline Media, accessed February 29, 2020. https://www.healthline.com/health/addiction/alcohol.
 Joseph Bennington-Castro, “What Is Alcoholism?,” Everyday Health, last modified September 13, 2016. https://www.everydayhealth.com/alcoholism/guide/.
 “Problem Drinking vs. Alcoholism: What’s the Difference?,” Talbott Recovery, accessed February 29, 2020. https://talbottcampus.com/problem-drinking-vs-alcoholism-whats-the-difference/.
 Chris Elkins, “Alcohol Facts and Stats,” DrugRehab.com, last modified February 28, 2020. https://www.drugrehab.com/addiction/alcohol/facts-and-stats/.
 Dan Schimmel, ed., “Why is alcohol addictive?,” QuitAlcohol.com, last modified May 16, 2019. https://www.quitalcohol.com/information/why-is-alcohol-addictive.html.
 “Alcoholism Statistics,” Treatment-Centers.net, accessed February 29, 2020. https://www.treatment-centers.net/addiction/drugs/alcohol/alcoholism-statistics.html.
 Lizmarie Maldonado, “Alcoholism Statistics and Important Facts,” ProjectKnow, Recovery Brands LLC, American Addiction Centers, accessed February 29, 2020. https://www.projectknow.com/drug-addiction/statistics/.
 “The Genetics of Drug and Alcohol Addiction,” Addictions and Recovery, accessed February 29, 2020. https://www.addictionsandrecovery.org/is-addiction-a-disease.htm.
 “What Is Caffeine Addiction?,” Caffeine Addiction and Abuse, Addiction Center, accessed February 29, 2020. https://www.addictioncenter.com/stimulants/caffeine/.
 Alina Petre, “Are Coffee and Caffeine Addictive? A Critical Look,” Healthline Media, last modified February 19, 2017. https://www.healthline.com/nutrition/caffeine-addiction#section2.
 “Nicotine: The Addictive Chemical in Tobacco Products,” U.S. Food & Drug Administration, last modified June 24, 2019. https://www.fda.gov/tobacco-products/health-information/nicotine-addictive-chemical-tobacco-products.
 Steven E. Meredith, Larua M. Juliano, John R. Hughes and Roland R. Griffiths, “Caffeine Use Disorder: A Comprehensive Review and Research Agenda,” Journal of Caffeine Research 3, 3 (September 2013): 114-130. https://dx.doi.org/10.1089%2Fjcr.2013.0016.
 Joseph Stromberg, “This Is How Your Brain Becomes Addicted to Caffeine,” Smithsonian Magazine, last modified August 9, 2013. https://www.smithsonianmag.com/science-nature/this-is-how-your-brain-becomes-addicted-to-caffeine-26861037/.
 Chelsea Greenwood, “Here’s why caffeine is so addictive – and why it’s so hard to give it up,” Insider, last modified August 1, 2018. https://www.insider.com/why-is-caffeine-addictive-2018-8.
 Elizabeth Hartney, “Caffeine Addiction Symptoms and Withdrawal,” Verywell Mind, last modified November 27, 2019. https://www.verywellmind.com/caffeine-addiction-4157287.
 Elizabeth Hartney, “What to Know About Caffeine Use,” Verywell Mind, last modified August 22, 2019. https://www.verywellmind.com/what-are-the-effects-of-caffeine-on-the-brain-21842.
 Karlee Weinmann, “Why We’re So Addicted To Coffee,” Business Insider, last modified October 29, 2011. https://www.businessinsider.com/two-things-make-coffee-irresistable-2011-10.
 “Caffeine Addiction Facts: How Addictive is Coffee vs. Cocaine?,” Clarity Way, last modified April 16, 2015. https://www.clarityway.com/addiction-recovery-blog/coffee-vs-cocaine-and-other-drugs-the-facts-about-addiction-might-surprise-you/.
 Jamie Ducharme, “How to Kick Your Caffeine Dependence for Good,” Time, last modified April 25, 2018. https://time.com/5245336/caffeine-addiction-caffeine-dependence/.
 Regina Boyle Wheeler, “Hooked on Caffeine?,” Everyday Health, last modified February 15, 2015. https://www.everydayhealth.com/addiction/hooked-on-caffeine.aspx.
 “Caffeine Addiction,” Luxury.Rehabs.com, Recovery Brands LLC, American Addiction Centers, accessed February 29, 2020. https://luxury.rehabs.com/caffeine-addiction/.
 “Why Is Sugar Addiction A Problem?,” Sugar Addiction, Addiction Center, accessed February 29, 2020. https://www.addictioncenter.com/drugs/sugar-addiction/.
 Anna Schaefer and Kareem Yasin, “Experts Agree: Sugar Might Be as Addictive as Cocaine,” Healthline Media, last modified October 10, 2016. https://www.healthline.com/health/food-nutrition/experts-is-sugar-addictive-drug#1.
 Elizabeth Hartney, “How Addictive Is Sugar Really?,” Verywell Mind, last modified February 4, 2020. https://www.verywellmind.com/sugar-addiction-22149.
 Dr. Joel Fuhrman, “Negative Impact of Sugar on the Brain,” Verywell Mind, last modified February 3, 2020. https://www.verywellmind.com/how-sugar-affects-the-brain-4065218.
 Magalie Lenoir, Fuchsia Serre, Lauriane Cantin and Serge H. Ahmed, “Intense Sweetness Surpasses Cocaine Reward,” PLoS ONE 2, 8 (August 2007): e698. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0000698.
 Nicole M. Avena, Pedro Rada and Bartley G. Hoebel, “Evidence for sugar addiction: Behavioral and neurochemical effects of intermittent, excessive sugar intake,” Neuroscience and Behavioral Reviews 21, 1 (2008): 20-39. https://dx.doi.org/10.1016%2Fj.neubiorev.2007.04.019.
 Dr. Viatcheslav Wlassoff, “Why Do We Become So Addicted to Sugar?,” PsychCentral, last modified July 7, 2018. https://psychcentral.com/blog/why-do-we-become-so-addicted-to-sugar/.
 “Can Sugar Be More Addictive Than Drugs?,” Ocean Breeze Recovery, accessed February 29, 2020. https://oceanbreezerecovery.org/blog/sugar-be-as-addictive-as-drugs/.
 “Sugar and Dopamine: The Link Between Sweets and Addiction,” Wellness Retreat Recovery Center, accessed February 29, 2020. https://wellnessretreatrecovery.com/sugar-and-dopamine-link-sweets-addiction/.
 Amy Reichelt, “Your brain on sugar: What the science actually says,” The Conversation, last modified November 14, 2019. https://theconversation.com/your-brain-on-sugar-what-the-science-actually-says-126581.
 “Sugar Addiction,” RehabSpot, Recovery Worldwide, accessed February 29, 2020. https://www.rehabspot.com/drugs/sugar-addiction/.
 Susan Raatz, “The Question of Sugar,” Agricultural Research Service, U.S. Department of Agriculture, last modified July 24, 2019. https://www.ars.usda.gov/plains-area/gfnd/gfhnrc/docs/news-2012/the-question-of-sugar/.
 “Is nicotine addictive?,” Tobacco, Nicotine, and E-Cigarettes, National Institute on Drug Abuse, accessed February 29, 2020. https://www.drugabuse.gov/publications/research-reports/tobacco-nicotine-e-cigarettes/nicotine-addictive.
 “Nicotine Dependence,” Mayo Clinic, accessed February 29, 2020. https://www.mayoclinic.org/diseases-conditions/nicotine-dependence/symptoms-causes/syc-20351584.
 Kathleen Raven, “Nicotine Addiction From Vaping Is a Bigger Problem Than Teens Realize,” Yale Medicine, last modified March 19, 2019. https://www.yalemedicine.org/stories/vaping-nicotine-addiction/.
 Leah Campbell, “Juuling: The Addictive New Vaping Trend Teens Are Hiding,” Healthline Media, last modified May 31, 2019. https://www.healthline.com/health-news/juuling-the-new-vaping-trend-thats-twice-as-addictive-as-cigarettes#1.
 Aseem Mishra, Pankaj Chaturvedi, Sourav Datta, Snita Sinukumar, Poonam Joshi and Apurva Garg, “Harmful effects of nicotine,” Indian Journal of Medical and Paediatric Oncology 36, 1 (2015): 24-31. https://dx.doi.org/10.4103%2F0971-5851.151771.
 Amber Erickson Gabbey, “Nicotine Addiction: What You Need to Know,” Healthline Media, last modified May 17, 2017. https://www.healthline.com/health/nicotine-and-related-disorders.
 Matt Gonzales, “Nicotine Addiction,” DrugRehab.com, last modified February 26, 2020. https://www.drugrehab.com/addiction/drugs/nicotine/.
 “Nicotine addiction: how long does it take to get addicted to nicotine,” Vaporesso, accessed February 29, 2020. https://www.vaporesso.com/blog/nicotine-addiction.
 Adam Felman, “What is nicotine dependence?,” Medical News Today, Healthline Media, last modified June 26, 2018. https://www.medicalnewstoday.com/articles/181299.
 Adam Felman, “What is addiction?,” Medical News Today, Healthline Media, last modified October 26, 2018. https://www.medicalnewstoday.com/articles/323465.