Breaking free of drug addiction is not easy no matter which substance you’re addicted to. However, some drugs may be harder to kick than others. Here’s what the most up-to-date research says are the hardest drugs to kick, listed in order from the most addictive to the least addictive.

Heroin

Many studies suggest that heroin is the most addictive substance of all. Derived from the opium poppy, heroin releases feel-good endorphins in the brain. Endorphins are natural brain chemicals that generate pleasure and counteract pain. Regular use of heroin shuts down the body’s endorphin system so that the addict can only feel good by using the drug. According to the National Institute on Drug Addiction, nearly 25 percent of those who try heroin become addicted to it. This category also includes other opiate painkillers like morphine and Demerol.

Crack Cocaine

Not to be confused with powdered cocaine, crack cocaine is a highly processed form of cocaine that’s smoked instead of snorted. Crack delivers a faster and more intense high than powdered cocaine, but the effect only lasts for about ten minutes. When smoked, crack brings on feelings of intense euphoria that are almost immediately followed by feelings of intense depression and an irresistible urge to use more.

Nicotine

Although it’s listed as the third-hardest drug to quit, nicotine doesn’t deliver an intense rush like heroin and crack. That might make it easier to kick. Still, nicotine still affects brain functioning enough that quitting generates physical, emotional, and mental discomfort.

Methadone

Methadone is a synthetic painkiller that’s used to treat heroin addiction. The only real difference between methadone and heroin is that the euphoric effects of methadone are less intense and last longer. Although it’s listed as the fourth-hardest drug to quit, many addiction specialists believe that methadone is even harder to kick than heroin. Like heroin, methadone shuts down the brain’s endorphin system so that addicts must take the drug to feel good.

Crystal Meth

Like crack, crystal meth primes your brain to want more. The high brings euphoria and jacks up energy, but when the drug wears off, the user feels drained and depleted. This low is so unpleasant that the addict is driven to consume more crystal meth just to feel normal.

Alcohol

Because it’s legal, socially approved and readily available, alcohol is not easy to quit. What’s more, unlike drugs, alcohol is a part of almost every social scene. Most people drink responsibly, stopping after a drink or two. This encourages alcoholics to think that they can do the same — even though they know they can’t.

Cocaine

Made from coca leaves, cocaine delivers a high-energy rush and a pleasurable high. Like crack and crystal meth, cocaine programs the brain to want more, and because the effects only last for about 30 minutes, users generally continue to snort the powder until the supply runs out.

Amphetamines

This central nervous system stimulant delivers a high that’s similar to crystal meth but milder and mellower. The effects last considerably longer than those of cocaine and crack. Amphetamines are highly addictive, and when taken regularly over an extended period of time, they can be very difficult to quit.

Benzodiazepines

Benzodiazepines are anti-anxiety medications like Valium and Xanax. These drugs are highly addictive and withdrawal can be dangerous. Withdrawal symptoms can include seizures and death.

It may be inaccurate to classify one drug as being more addictive and difficult to kick than another. The most important factor in kicking any drug may have more to do with how much an addict wants to recover than on how difficult a drug is to quit.