Ever since Toronto Mayor Rob Ford admitted to having smoked crack cocaine, various city councillors and media observers have publicly advised him to seek drug counselling. But in a CNN interview that aired Nov. 18, Ford continued to stand by his message: “I’m not an addict.”

The ongoing saga of the mayor’s crack use has raised unanswered questions about how addictive the drug really is.

It’s been commonly accepted that crack is more addictive than other drugs, but addictions researchers and drug counsellors say it’s hard to compare the addictiveness of specific substances because drug-taking is a highly individual experience.

Is it possible to smoke crack once and walk away?

Robin Haslam, director of operations and procedures for Addiction Canada, says that he has never met someone who can “just casually smoke crack.” However, people have different thresholds of addiction.

“I know people who have used crack once, and never touched it again. I also know people who smoked marijuana once, and became very impaired,” he says.

Carl Hart, author of High Price: A Neuroscientist's Journey of Self-Discovery That Challenges Everything You Know About Drugs and Society, told CBC Radio’s Day 6 that crack “is not uniquely addictive, or it’s not something that is special, as we have all been taught.”

Hart said that the percentage of people that become addicted to crack is lower than most think. “For example, 10 to 20 per cent of people will become addicted — that means that 80 to 90 per cent of people won’t become addicted.”

Crack emerged as a concern in the 1980s

Crack is a smokeable form of cocaine that is typically prepared by condensing cocaine and baking soda into a “rock.” It first emerged in large U.S. cities in the early 1980s.

In 1986, Time magazine called crack “an inexpensive yet highly potent, highly addictive form of cocaine” that was rapidly spreading across America. This contributed to crack’s reputation as being among the most addictive drugs.

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Police say each packaged tablet of crack cocaine sells at about $10 on the street. ((CBC))

Numerous studies and advocacy groups on the internet rank drugs by addictiveness, but they don’t all reach the same conclusion about which is the most addictive.

Two studies in particular — one from 1994 and one from 2010 — are often cited as credible drug ranking systems.

In 1994, Jack Henningfield, a professor at the Johns Hopkins University School of Medicine in Baltimore, Md., attempted to compare drugs in a study on addiction and cigarette smoking. He developed the “Henningfield rating scale” for five factors of harm: withdrawal severity, habit forming, tolerance, dependence and intoxication.

“These are subjective ratings meant to help explain to people that all addictive drugs are not the same. If you just look at any one feature, you can put some drugs higher or lower on the scale,” says Henningfield.

Dependence is only one part of addiction

The Henningfield scale ranked nicotine highest in the dependence category, followed by heroin, cocaine, alcohol, caffeine and marijuana.

Haslam says that dependence is one of the key indicators of addiction, but it is not the only one. For example, a person with type I diabetes can be dependent on, but not addicted to, insulin.

“In addiction, the person gets to a level [of dependence] where they knowingly administer the drug to themselves, knowing that it is causing them harm,” says Haslam.

He says that substance abuse and the rate of developing a dependency to any drug is a very personal thing. Family dynamics, socio-economic background, educational background, gender and culture are all important factors in the likeliness of someone developing a dependency to a drug.

Jack Daniel's Bottle Dispute

Alcohol is ranked the most harmful substance to both the individual and to others, in UK study in 2010. (The Associated Press)

In 2010, David Nutt and his colleagues on the Independent Scientific Committee on Drugs in the U.K. integrated many of these factors into a more sophisticated analysis than the Henningfield rating scale.

This study ranked the overall harm of 20 drugs using 16 criteria.

In this study, the criteria were assigned different weights, or importance, to give a more realistic model of the overall harm to U.K. society from each drug, said Nutt, professor of neuropsychopharmacology at the Imperial College in London.

The criteria included drug-related health and mortality risks, dependence, loss of possessions and relationships, crime, health care costs and environmental damage in production of the drug.

Alcohol is ranked as the most harmful substance in this study in terms of overall harm to both the individual and to others.

Dependency, defined in this study as “the extent to which a drug creates a propensity or urge to continue to use despite adverse consequences,” ranks crack cocaine highest, followed by tobacco, heroin and methamphetamines as the most dependence-forming substances. Alcohol is ranked tenth.

Crack addiction rates are decreasing

Rebecca Jesseman, a research and policy analyst at the Canadian Centre on Substance Abuse, said that crack cocaine “tends to be a fairly highly stigmatized drug.”

She said that “some of those same stimulant properties [of crack] are experienced, but for a longer duration, in many of the amphetamines.”

Haslam says that the “most addictive drug in Canada [today] is not a street drug, it’s opiates — prescription drugs like codeine.”

According to Health Canada’s 2012 alcohol and drug use monitoring survey, about 78 per cent of adults over age 15 drank alcohol in the year before the survey; 10 per cent used marijuana; one per cent used hallucinogens (such as LSD or mescaline) and one per cent used cocaine or crack.

Jesseman said that crack use overall has been on the decline.

“For Canadians, and actually internationally over the last about 10 years, the rates of [crack] use have been decreasing,” she said.

She said this drop is a combination of availability, price, reputation and competing substances.

While Haslam says that crack use is obviously of great concern, most of the people that his organization sees are using multiple substances.

“Addiction Canada rarely, if ever, sees a client that is only addicted to a single drug. There’s always something else that goes with it,” Haslam says.

Addictions counsellors focus on the individual and don’t pay too much attention to studies that rank addictiveness.

 “I don’t really care what the drug is if it affects your ability to function,” says Haslam.