The technical definition of a drug is “any chemical substance that affects the central nervous system.” Determining the most addictive drugs has been a challenge for researchers and results have been controversial throughout the years. Additionally agreeing on a proper definition for “addiction” and criteria by which it can be measured is somewhat difficult.
The number one most harmful drug seems to be alcohol as measured by cumulative societal damages, but the most addictive drug is relatively unclear. Most sources suggest heroin, while others suggest that nicotine, crystal meth, and crack may be just as, if not more addictive. In the early 2000s, researcher named David Nutt from London’s Imperial College came up with an idea to study the harm from drugs, in which he also examined addictive properties.
He compared addictive properties of various drugs by measuring ratings of: pleasure, psychological dependence, and physical dependence. These ratings were measured on a scale of “0” (being least addictive) to “3” (highest level of addiction). He then took an average of the pleasure, psychological, and physical dependence scores and came up with a mean composite score for each of the 20 drugs.
His results for a few substances were contrary to what the government and general public wanted to hear: alcohol and tobacco were more addictive than marijuana and ecstasy. The backlash he endured as a result of his study lead to his firing as the leading UK drug adviser. The results of his study are still regarded by many as being the most accurate. In attempt to validate and expand upon his research, some sources suggest that a team of Dutch scientists conducted a similar study; unfortunately there appears to be no valid citation for this similar study.
10 Most Addictive Drugs List: Objective Rankings
When it comes to determining the most addictive drugs, there is still a general lack of research. The best study on the subject was published in 2007 by David Nutt in the Lancet called “Development of a rational scale to assess the harm of drugs of potential misuse.” A majority of the results in the rankings below are based off of his study. However, a couple more specific drugs included in the Dutch research were also taken into consideration.
1. Heroin (diacetylmorphine)
- Addiction rating: 3.0 – In the newer study, a slightly reduced rating of 2.89 was given.
If you asked the average person what they thought the most addictive drug was, most would probably guess heroin – and according to a majority of data, they would be correct. According to the Henningfield Ratings and Benowitz Ratings which measure a drug’s addiction potential based on: withdrawal, reinforcement, tolerance, dependence, and intoxication – both rank heroin as the most addictive drug.
Heroin is considered an opioid analgesic drug that was developed in the 1870s by combining acetyl groups with the molecule morphine. The chemical “heroin” itself doesn’t have any effect, but when ingested by the body, it converts into morphine, and gives users a significant psychological and physical high. It acts as a depressant on the central nervous system, slowing down functioning throughout the body.
What makes heroin so addictive? Regular usage of heroin causes an individual to develop a rapid tolerance and dependence. Its usage is associated with feeling of significant euphoria with simultaneous deep relaxation. The combination of the euphoria and deep relaxation makes people feel on top of the world and provides a lucrative escape from the emotional pain and stress of everyday life.
Heroin also crosses the blood-brain barrier rapidly and binds to the mu-opioid receptors. It is the binding to these receptors that leads a person to feeling significant amounts of euphoria. In addition to inducing extreme euphoria and acting as an anxiolytic, it also acts as an analgesic, providing a significant degree of pain relief.
What separates heroin from other prescription pain medications is that it also results in a greater release of the neurotransmitter histamine. This histamine release gives the person using it a greater overall physical “high.” Using heroin on a consistent basis is thought to change functioning of the opioid receptors so that when a person stops using it, they experience anxiety, muscle spasms, insomnia, and general sickness. (Read: Heroin withdrawal symptoms).
2. Cocaine / Crack Cocaine
- Addiction rating: 2.39 – In the newer Dutch study, they specifically examined crack cocaine, and found its addictive properties to be greater than standard forms such as powder cocaine. Their rating specifically for crack cocaine was 2.82.
Crack cocaine refers to the form of freebase cocaine that is often smoked. Smoking crack cocaine allows the drug to be delivered to the brain quicker than snorting or other forms of administration. The effect of crack cocaine is considered similar to that of standard cocaine, but it gets you higher quicker compared to standard forms of cocaine – almost like drinking vodka as opposed to beer to get drunk – the effect is achieved quicker with crack.
Cocaine gives the user an intense high that is characterized by euphoria and stimulant effects on the central nervous system. Those who smoke crack are likely to feel increased social confidence, energetic, more alert, and in some cases, as if they are on top of the world. These effects are achieved by the drug acting as a dopamine reuptake inhibitor, particularly via blocking the dopamine transporter.
A large quantity of dopamine accumulates between neurons (within the synaptic cleft) when a person smokes crack or uses cocaine. Upon accumulation of dopamine between synapses, this transient dopaminergic spike allows the user to feel an extreme sense of pleasure, focused, and stimulated. Tasks that were previously mundane may seem highly entertaining. The high that is obtained from smoking isn’t typically long lasting (10 to 15 minutes) compared to that of snorting (20 to 30 minutes).
Although the high is considered relatively short from cocaine, it is so rewarding that people want to experience more of it. Additionally when the high wears off, an inevitable “crash” is inevitable in which dopamine levels experience a significant drop-off. This results in the exact opposite effect of what the person experienced while they were “high.” In order to avoid this crash, many people seek out another cocaine high.
With each consecutive usage of crack cocaine, dopamine levels continue to drop – preventing a person from feeling as euphoric as their first time using. Unfortunately without replenishment of dopamine, this turns into a downhill spiral and the user becomes dependent on the drug for functioning or feeling normal. According to the composite Benowitz Ratings for drug addiction, cocaine is only marginally less addicting than heroin. (Read: Cocaine withdrawal symptoms).
- Addiction rating: 2.21 – In the new Dutch study, this was given a rating of 2.82, which would be equivalent to that of crack cocaine.
When nicotine is mentioned, most people think of tobacco products. Since tobacco products are legal, the common misconception is that they must be less addicting than all illicit drugs. If that were true, the Henningfield Rating of addiction for nicotine wouldn’t be nearly equal to that of cocaine and there would be significantly less people buying cigarettes.
Although you may not think that nicotine is as damaging as cocaine, the fact is that nearly 20% of deaths each year in the United States are a result of tobacco products – all of which contain nicotine. If we do the math, that means over 1,000 people are dying in the United States each day from deaths resulting from nicotine.
Nicotine is a considered a very potent stimulant and is derived from the Solanaceae plant. At high doses of nicotine can be poisonous, while at lower doses (those used in tobacco products) it produces stimulating effects. When ingested, it crosses the blood-brain barrier binds to various acetylcholine receptors as both an agonist and antagonist.
It tends to have a direct effect on cholinergic receptor activity and is thought to influence neurotransmission of dopamine and production of epinephrine. The degree to which it affects dopamine is thought to improve cognition, increase relaxation, and give the user a slight “buzz” characterized by slight euphoria. As a person continues to smoke, their receptors become desensitized to the chemical, and people experience “cravings” for the buzz that they get from the nicotine.
In the brain of smokers, monoamine oxidase activity is reduced, leading to less dopamine getting broken down, which promotes increased craving for products containing nicotine. Although the degree of intoxication from nicotine is substantially less than that of heroin or crack cocaine, it can be as physically as addictive as both substances. Nicotine hijacks the reward system in our brain, and demands that we ingest more of it to feel satisfied.
People have a difficult when they try to quit smoking because the reward center in the brain becomes hypersensitive to the lack of nicotine. This results in periodic cravings throughout the day that are difficult to resist. The neurochemistry changes in the brain that occur as a result of nicotine usage can take months of being drug-free to naturally correct. (Read: Nicotine withdrawal symptoms).
4. Street Methadone
- Addiction rating: 2.08 – In the original study by Nutt, it was suggested that “Street Methadone” is more potent than standard formulations. The rating in the Dutch study gave Methadone a 2.68 rating.
Methadone is a drug that is commonly used for opioid replacement therapy and sometimes minor pain management. It is generally prescribed to an individual that is attempting to get off of a more extreme opioid like heroin or high dosages of pain pills. The theory is that by transitioning from the more potent drug to methadone, a person won’t experience as severe of a withdrawal.
It is suggested that Methadone works as a mu-opioid agonist and also binds to the NMDA glutamate receptor, acting as an antagonist. The NMDA antagonism contributes to decreased opioid cravings and reductions in tolerance among opioid addicts. Due to the sheer potency of methadone at replicating many effects of opioids, it is easy for an individual to build a tolerance and become addicted.
This drug also affects the body’s natural ability to produce endorphins and is thought to influence various neurotransmitters such as dopamine. Although it may seem better to take methadone to avoid extreme withdrawals from another substance, many people become just as addicted to the methadone as they did their original opioid. Methadone can be helpful, but it’s analogous to choosing a (slightly) lesser of two evils.
Many people visit methadone clinics and get relief from the drug, but end up becoming nearly as addicted to methadone as they did the original opioid that caused them problems. There are cases of people taking methadone for years because they cannot bring themselves to face the withdrawal. (Read: Methadone withdrawal).
5. Crystal Meth (d-methamphetamine)
- Addiction rating: N/A – David Nutt’s research didn’t specifically single out “crystal meth” compared to standard amphetamine. In the newer Dutch study it received a rating score of 2.24 – suggesting that it’s highly addictive. Since the newer research has been relatively similar to David Nutt’s in terms of rankings, this substance was strategically placed at #5 on the list.
Crystal meth is a synthetic stimulant that when taken, generates feelings of artificial euphoria. In comparison to the powder formulation of methamphetamine, crystal meth is considered to be of increased potency. Although completely odorless, it significantly increases activity in the central nervous system.
In the short term, crystal meth can make people believe they are highly powerful and they feel unstoppable. Effects people commonly experience over the short term include aggression, irritability, and hyperactivity. Over the long term, this drug can change blood pressure, damage blood vessels, and in some cases, even cause death.
Crystal meth and other forms of methamphetamine are able to flood the brain with abnormally high levels of dopamine. Dopamine has an influence on mood, pleasure, and arousal. When dopamine is increased from the crystal meth, it is significantly greater than what is naturally possible. Since the user feels such a high from the dopamine release, they continue to seek out that same level of euphoria.
Over time, dopamine receptors become depleted and the brain’s baseline levels of dopamine drop. It takes a significant amount of time for the dopamine and dopamine receptors to restore themselves. Since there is a significant time gap with a dopamine deficiency, a person will continue to seek out the drug in order to feel good in the short-term, but essentially digging themselves in a deeper hole – one that can be impossible for some to escape.
- Addiction rating: 2.01
Barbiturates drugs that depress activity in the central nervous system and can lead to a variety of different effects. In some cases, they lead to anxiolytic and sedative effects, while in other cases they have more extreme anesthetic effects. These days they are seldom prescribed by doctors as a result of their high potency, which exceeds that of benzodiazepines.
In addition to inducing significant relaxation and sleepiness, they also have minor analgesic (pain-relieving) properties. The addiction potential of these drugs is considered high in part due to the rapid development of tolerance. They function primarily on the GABA receptors and can lead users to experience feelings of “euphoria” during their high.
It should be noted that the tolerance developed from this class of drugs is different than that of alcohol and benzodiazepines. Perhaps you’ve heard of Seconal or Nembutal – two common examples of barbiturate drugs. The addiction rating of this drug is somewhat disputed based on current research, but in the original study by David Nutt, these were more addictive than alcohol.
- Addiction rating: 1.93 – The newer Dutch rating gave alcohol a 2.13 rating.
It seems as though nearly everyone likes kicking back on the weekend and cracking open a few beers. When going out to restaurants, most adults end up getting some sort of alcoholic beverage. Alcohol is a completely legal substance and due to its widespread use and legality, most people underestimate its addiction potential.
In terms of intoxication, alcohol is has the highest rating on both the Henningfield and Benowitz scales. As a composite ranking, it is considered to be even more addicting than nicotine. If both composite scores are averaged, it would even be regarded as slightly more addicting than cocaine. Additionally withdrawal from alcohol can be deadly compared to many other drugs.
Withdrawing from an opioid may be highly unpleasant, but it usually isn’t fatal. Alcohol withdrawal on the other hand can be highly fatal. Alcohol is a central nervous system depressant that affects motor skills and alters the brain’s reward system. It allows the drinker to feel pleasure, decreased fear of rejection, increased social confidence and significant anxiolytic effects.
As a result of being completely legal in the United States for individuals 21 years of age or older, over 17 million Americans are thought to have an alcohol-related disorder. In terms causing harm in society, alcohol is considered the most harmful. Despite being highly addicting, many people have found ways to overcome their addiction (such as through organizations like Alcoholics Anonymous).
- Addiction rating: 1.83 – The newer study suggested 1.89 which turns out to be a slight increase.
You’ve probably heard of Xanax or Valium – these are classified as benzodiazepines, or sedative hypnotic drugs. They decrease activity in the central nervous system by acting on the neurotransmitter GABA in the brain. This essentially decreases excitability and yields potent anxiolytic effects – which is why benzos are considered the most effective class of anxiolytic and panic attack medications.
However, when a person consistently uses these drugs, tolerance is quickly established. This means a person will continuously need to take more of the drug to feel the same initial anxiolytic effect. It is the extreme relaxation that can be felt while on benzodiazepines that make them so addicting. When used properly and on an “as needed” basis, the likelihood of addiction drops. When individuals are using them every day in order to cope with the stressors of life, addiction becomes a real problem.
These are also some of the most difficult drugs to quit because the withdrawal process tends to result in even worse anxiety than a person experienced prior to taking the drug. This is because GABA levels in the brain have become depleted and need to be reestablished. Benzo withdrawal can also be deadly if a gradual taper is not conducted.
For certain individuals, these drugs are as addicting as any and in terms of danger – these drugs are linked to developing dementia. The argument could easily be made that these are more addicting than their addiction rating suggests.
9. Standard Amphetamines (Pure or Mixed Salts)
- Addiction rating: 1.67 – The newer rating in the Dutch study gave a 1.95 rating to amphetamine.
Amphetamines are common stimulants of the central nervous system that can be used recreationally to achieve a buzz, but are medically used to treat ADHD and wakefulness disorders such as narcolepsy. Amphetamine was discovered in the late 1880s and is exists in the form of multiple stereoisomers, namely “levo” and “dextro” amphetamine. Amphetamine generally refers to mixed formulation of these stereoisomers.
Individuals that use amphetamines can become quickly addicted to the effects. Most people notice an improvement in mood, pro-social behavior (e.g. increased talkativeness), accompanied by an energy increase and boost in cognition. The stimulating high from amphetamines is created when the drug alters neurotransmitter signaling in the reward pathways and executive areas of the brain.
In other words, more dopamine and norepinephrine are produced – in relationship to the dose someone takes. When someone takes a high dose of an amphetamine, they will likely experience a euphoria from the heavy release of dopamine. However, since tolerance is quickly established on these drugs, the euphoria tends to fade over time, requiring a greater dosage to feel the same initial effect.
When people stop using these drugs, most experience a significant crash – characterized by sleepiness, increased appetite, reduced levels of dopamine, and low arousal. (Read: Adderall crash). In addition to becoming addicted to the psychological high that can be obtained from amphetamines, some individuals also become addicted to the favorable side effects including: increased concentration and productivity, weight loss, and increased energy.
- Addiction rating: 1.64 – The newer Dutch study failed to mention this particular drug.
Used medically for the same purpose as methadone, buprenorphine is used for the purpose of opioid replacement therapy, or to help ease the transition off of harder drugs like heroin. It works by acting as a partial agonist of the mu-opioid receptor and an antagonist at other opioid receptor sites (kappa and delta). It is also used in some cases in management of moderate pain at smaller doses.
Like methadone, people often go on buprenorphine and like the fact that they don’t have to go through the physical withdrawal associated with opioids. However, many people end up making the transition to this drug and become so addicted to its effects that they cannot stop. Although in formulations like Suboxone, there is a ceiling effect – meaning after a certain dose is reached, no more stimulation occurs, people often become dependent on it for functioning.
In addition to being used by opioid addicts to help beat their addiction, it is also sometimes prescribed off-label to treat depression. (Read: Suboxone for depression). Many people have found that they experience a significant enhancement of overall wellbeing and experience elevated mood as a result of taking this drug. The problem is that once the body and brain adapt to this drug, it can be an absolute nightmare to withdraw from. (Read: Suboxone withdrawal symptoms).
Comparison: David Nutt’s (2007) research vs. Dutch findings…
There are several similarities and differences between the initial research conducted by David Nutt and that brought forth in the alleged (elusive) Dutch study. Both agree on the most addictive drug, but other rankings differ slightly. The Dutch study seemed to get into more specifics, whereas the original focused more on general classifications.
Similarities: Both David Nutt and the Dutch study seem to agree that the most addictive drug of all is heroin. If we are generalizing, both do find various forms of cocaine to be the second most addicting, and nicotine to rank third on the addiction scale.
Differences: The studies differ in various drug rankings and ratings. The Dutch study seems to have standard forms of cocaine ranking lower on the scale than alcohol. Additionally in the Nutt study, specific formulations of drugs such as “crystal meth” or “crack cocaine” are not mentioned. One striking difference was the mention of GHB in the newer study as being ranked #10 and in the older Nutt study, being among the least addictive drugs. Since there’s no formal citation for this newer research, I gave more weight to the published study by Nutt.
Other scales: There are other scales that attempt to measure addictive potential such as the Henningfield and Benowitz ratings. These compare six common substances and assess their addiction potential. Respectively Dr. Jack E. Henningfield is from the National Institute on Drug Abuse and Dr. Neal L. Benowitz is from the University of California at San Francisco. They based their addiction potential on five criteria including: withdrawal, reinforcement, tolerance, dependence, and intoxication. I took the personal liberty of averaging these five rating scores (which were given on a scale of 1 to 6). The lower the overall composite score, the greater the addiction potential.
- Heroin (9)
- Alcohol (12)
- Cocaine (15)
- Nicotine (15)
- Marijuana (27)
- Caffeine (27)
- Heroin (10)
- Cocaine (11)
- Alcohol (13)
- Nicotine (18)
- Caffeine (22)
- Marijuana (26)
Other information to consider…
When thinking about how addictive a particular drug is, other factors may need to be considered. This includes things like: how the drug is administered and validity of the rating scales used.
- Administration: How is the person taking the drug? Are they snorting it, smoking it, injecting it, using a transdermal patch, etc.? There are many different ways to take a particular drug, and certain methods of administration have been thought to increase likelihood of addiction. For example, the ritual associated with self-injection of heroin is thought to be highly addicting compared to administration of heroin by a medical professional in a hospital setting.
- Accuracy of rating scale: How valid are these rating scales that are being used to determine a composite score for addiction potential? Without more studies being conducted and discrepancies between current studies, it may be important to question the validity of these ratings.
- Individual variation: It is also important to realize that there is always the possibility for individual variation. For example, one person may have tried all of the drugs on this list and may become addicted to one with a lower rating score and may not become addicted to one with a high rating score. The above ratings are meant to be used as a general rule of thumb. Certain people may have an easy time kicking a more addictive drug than one lower on the list, which would suggests individual differences.
- Severity of withdrawal: Some individuals seem to think that severity of withdrawal is a direct reflection of the degree to which a drug is addictive. Although in some cases there is a correlation, other times there isn’t.
Most people have a general idea of what drugs are highly addictive and what one’s aren’t. This scale helps put things into perspective and helps people get a more accurate estimation of the truth. However, it cannot be assumed that even this list is completely accurate. More research needs to be conducted in this area in order to verify or nullify the presented hierarchy.
Having personally used several drugs on this list including: methadone, benzodiazepines, alcohol, and amphetamines, it seems as though the order is subjectively accurate in my experience. If there was one change I’d make for the drugs that I’ve used, I would probably move benzodiazepines ahead of alcohol.
Further research is warranted in ranking addictive drugs
Currently we lack a comprehensive reference for addiction potential of various drugs. In the past, most researchers only examined the addiction potential of nicotine, heroin, cocaine, alcohol, caffeine, and marijuana. This list is a bit more comprehensive because it provides some insight in regards to specific drug subtypes such as “crack cocaine” and “crystal meth” but also fails to provide specific pharmaceutical drugs.
I would venture to believe that a drug such as OxyContin which provides 12 hours of release of Oxycodone would make the list. It would also be interesting to compare specific drugs such as Valium and Xanax and have a ranking hierarchy within each broad class of drugs. Although most drugs act similarly, there are going to be slight differences. What do you think about the list of drugs above? Feel free to share your thoughts and personal experiences in the comments section below.