Approximately 30% of the population of the Human Species has the series of genetic factors colloquially known as "The Addiction Gene". If you lack the "Addiction Gene", you can become Chemically DEPENDENT upon a substance and suffer from withdrawal when abstaining from a substance that you build a tolerance to but you can't become "Addicted".
"Addiction" is the inability to quit despite mounting consequences and the fixation and intrusive craving for said substance or activity after withdrawal.
That 30% of approximately 7 billion humans are ALL capable of becoming Addicted to Alcohol, Opiates, etc. but of that 30%, only 9% are physically and mentally capable of becoming addicted to Marijuana.
30% of 7 billion = 2,100,000,000
9% of 2,100,000,000 = 189,000,000
Meaning, 2,100,000,000 can be addicted to alcohol but only 189,000,000 can become addicted to Marijuana and yet Marijuana is listed as more dangerous and addictive (legally) as Cocaine.
YES, MARIJUANA IS ADDICTIVE TO A SMALL PERCENTAGE OF PEOPLE THAT HAVE THE GENETIC POTENTIAL FOR ADDICTION.
There is NO SUCH THING as "Mentally Addictive". You are your brain, your brain is what is altered by drug use. Period.
Marijuana effects different people differently, based on their specific biology. Some people get super happy and bouncy, some get depressed and tired, some get panic attacks.
Long term use has been shown to lead to a "Tolerance" in people that have the biology of addiction. It also eventually starts to trigger mental health issues in these people. After up to 15 years of chronic use (no pun intended) the way the canabanoides work in the addict's brain alters and they stop feeling "Good" so they start to use more trying to find that good feeling again and will eventually seek another means of affect regulation since they have been self medicating. They switch to Alcohol, Meth, Ecstasy, etc. because they work in the brain similarly to Marijuana. This leads to REALLY SUPER BAD addiction problems.
"When they say it's not addictive, it means you can't get physically addicted where you would ever go through withdrawal if you didn't have it."
There is a withdrawal. Period. End of story. The withdrawal and the time it takes for the brain to return to "Normal" can take months and the suicidality of people abstaining after long term use and addiction is super high. The main complaint is severe sleep problems and severe depression. This is why marijuana needs TREATMENT when addiction occurs because it is as profound as heroin addiction.
Of course, this is only relevant to approximately 189,000,000 people on EARTH.
The rest of us can use it without complaint because we lack the genetics to become addicted to Weed.
If you really want to know about it, look up these documentaries.
BBC Horizon Cannabis: The Evil Weed?
The Corporation: The Business of Getting High
Hooked: Illegal Drugs & How They Got That Way.