Eight states have legalized adult (aged 21 and older) personal use of marijuana and legally regulate the production, distribution, and sale of marijuana: Alaska, California, Colorado, Maine, Massachusetts, Nevada, Oregon, and Washington state. Additionally, the state of Vermont and the District of Columbia have legalized limited personal possession and cultivation of marijuana by adults aged 21 and older.

"The gateway effect, if it exists, has at least two potential and quite different sources (MacCoun, 1998). One interpretation is that it is an effect of the drug use itself (e.g., trying marijuana increases the taste for other drugs or leads users to believe that other substances are more pleasurable or less risky than previously supposed). A second interpretation stresses peer groups and social interactions. Acquiring and using marijuana regularly may lead to differentially associating with peers who have attitudes and behaviors that are prodrug generally, not only with respect to marijuana. One version of this is the possibility that those peers will include people who sell other drugs, reducing the difficulty of locating potential supplies. If the latter is the explanation, then legalization might reduce the likelihood of moving on to harder drugs compared to the current situation."

"Tetrahydrocannabinol is a very safe drug. Laboratory animals (rats, mice, dogs, monkeys) can tolerate doses of up to 1,000 mg/kg (milligrams per kilogram). This would be equivalent to a 70 kg person swallowing 70 grams of the drug—about 5,000 times more than is required to produce a high. Despite the widespread illicit use of cannabis there are very few if any instances of people dying from an overdose. In Britain, official government statistics listed five deaths from cannabis in the period 1993-1995 but on closer examination these proved to have been deaths due to inhalation of vomit that could not be directly attributed to cannabis (House of Lords Report, 1998). By comparison with other commonly used recreational drugs these statistics are impressive."

"Marijuana essentially became illegal in 1937 pursuant to the Marijuana Tax Act.³⁹ The use of marijuana required the payment of a tax for usage; failure to pay the tax resulted in a large fine or stiff prison time for tax evasion.⁴⁰ Drug prohibition was elevated to another level by targeting 'marijuana,' a plant that had never demonstrated any harm to anyone.⁴¹
"Anslinger’s [Harry J. Anslinger, the first Commissioner of the Federal Bureau of Narcotics] efforts to eradicate marijuana continued when Anslinger sought similar anti-narcotic laws against marijuana at the state level.⁴² Guided by Anslinger’s policy direction, states began passing their own laws or adopting more strident versions of federal laws.⁴³ By 1952, nearly all states had anti-narcotic laws in place.⁴⁴"

"Several meta-analyses of multiple studies found that the risk of being involved in a crash significantly increased after marijuana use¹³ -- in a few cases, the risk doubled or more than doubled.^14-16 However, a large case-control study conducted by the National Highway Traffic Safety Administration found no significant increased crash risk attributable to cannabis after controlling for drivers’ age, gender, race, and presence of alcohol.¹⁷"

Although the intent of a 'War on Drugs' may have been to target drug smugglers and 'King Pins,' according to the FBI's annual Uniform Crime Reports, of the 1,488,707 arrests for drug law violations in 2015, 83.9% (1,249,025) were for mere possession of a controlled substance. Only 16.1% (239,682) were for the sale or manufacturing of a drug. Further, the majority (43.2%) of drug arrests in 2015 were for marijuana -- a total of 643,121. Of those, an estimated 574,641 arrests (38.6% of all drug arrests) were for marijuana possession alone. By contrast in 2000, a total of 734,497 Americans were arrested for marijuana offenses, of which 646,042 (40.9%) were for possession alone.

"The law enforcement view of marijuana was indelibly shaped by the fact that it was initially connected to brown people from Mexico and subsequently with black and poor communities in this country. Police in Texas border towns demonized the plant in racial terms as the drug of 'immoral' populations who were promptly labeled 'fiends.'

"As the legal scholars Richard Bonnie and Charles Whitebread explain in their authoritative history, 'The Marihuana Conviction,' the drug’s popularity among minorities and other groups practically ensured that it would be classified as a 'narcotic,' attributed with addictive qualities it did not have, and set alongside far more dangerous drugs like heroin and morphine.

"By the early 1930s, more than 30 states had prohibited the use of marijuana for nonmedical purposes. The federal push was yet to come.

"The stage for federal suppression of marijuana was set in New Orleans, where a prominent doctor blamed 'muggle-heads' — as pot smokers were called — for an outbreak of robberies. The city was awash in sensationalistic newspaper articles that depicted pushers hovering by the schoolhouse door turning children into 'addicts.' These stories popularized spurious notions about the drug that lingered for decades. Law enforcement officials, too, trafficked in the 'assassin' theory, under in which killers were said to have smoked cannabis to ready themselves for murder and mayhem."

The Times misses part of the story when they write:
"Nearly 70 percent of the teenagers in residential substance-abuse programs run by Phoenix House, which operates drug and alcohol treatment centers in 10 states, listed marijuana as their primary problem."
http://www.nytimes.com...

Indeed. However, the majority of treatment referrals for marijuana were directly through the criminal justice system or at least in anticipation of going through the criminal justice system. Treatment alternatives to incarceration and drug courts can be effective means of dealing with drug using offenders yet they sometimes cherry-pick people to be referred to treatment, choosing those with the greatest probability of success. People who do not use drugs problematically are the most likely to succeed in drug treatment, since they didn't have a problem in the first place:
"Additional results reveal that, in practice, large numbers of drug courts are admitting offenders who are abusing alcohol and marijuana, but may not be clinically dependent or abusing more serious drugs. Consistent with the number of courts admitting individuals with lower levels of substance use and the number admitting individuals with DWI/DUI offenses, 65.6 percent of courts reported that a participant can be admitted into drug court for alcohol abuse only. An even larger percentage of courts (87.7 percent) indicated that participants can enter drug court for marijuana abuse only. Allowing participants into drug court based on alcohol abuse only did not vary by type of geographic area; however, allowing participants into drug court based on marijuana abuse only did vary geographically (X2=10.2, p<.01). The majority of courts that do not accept participants into drug court based only on marijuana abuse are located in urban areas (62.2 percent), suggesting they may have a greater focus on more serious drug problems."
Source: Rossman, Shelli B., et al., "Final Report, Volume 2: The Multi-Site Adult Drug Court Evaluation: What's Happening with Drug Courts? A Portrait of Adult Drug Courts 2004" (Washington, DC: Urban Institute, June 2011), p. 27.

According to the federal Treatment Episode Data Set, in 2011 there were 333,578 admissions to treatment with marijuana reported as the primary substance of abuse out of the total 1,844,719 admissions for all substances that year.
According to the TEDS report:
"• Marijuana was reported as the primary substance of abuse by 18 percent of TEDS admissions aged 12 and older in 2011 [Table 1.1b].
"• The average age at admission for primary marijuana admissions was 24 years [Table 2.1a], although the peak age at admission for both genders in all race/ethnicities was 15 to 17 years [Figure 12]. Forty percent of marijuana admissions were under age 20 (vs. 11 percent of all admissions), and primary marijuana abuse accounted for 74 percent of all admissions aged 12 to 14 years and 76 percent of admissions aged 15 to 17 years [Tables 2.1a-b].
"• Non-Hispanic Whites accounted for 45 percent of primary marijuana admissions (32 percent males and 13 percent females), and non-Hispanic Black males accounted for 24 percent [Table 2.3a].
"• Twenty-five percent of primary marijuana admissions had first used marijuana by age 12 and another 32 percent by age 14 [Table 2.5].
"• Primary marijuana admissions were less likely than all admissions combined to be self- or individually referred to treatment (16 percent vs. 35 percent). Primary marijuana admissions were most likely to be referred by a criminal justice/DUI source (52 percent) [Table 2.6].
"• More than 4 in 5 marijuana admissions (85 percent) received ambulatory treatment compared with about 3 in 5 of all admissions combined (62 percent) [Table 2.7].
"• Fifty-six percent of primary marijuana admissions reported abuse of additional substances. Alcohol was reported by 41 percent [Table 3.8]."
Source: Substance Abuse and Mental Health Services Administration, Center for Behavioral Health Statistics and Quality. Treatment Episode Data Set (TEDS): 2001-2011. National Admissions to Substance Abuse Treatment Services. BHSIS Series S-65, HHS Publication No. (SMA) 13-4772. Rockville, MD: Substance Abuse and Mental Health Services Administration, 2013, p. 19; and p. 43, Table 1.1a.

"Preliminary look at racial disparities in select counties of Washington

"The Crime, Cannabis & Police Research Group at Washington State University used preliminary data from a Department of Justice funded study to compare white vs. Black arrests.11 Latinos were not included in the analysis, because of difficulties measuring ethnicity in arrest data. Their main preliminary findings are that after legalization in Washington, African Americans/Blacks continue to be disproportionally arrested for the possession and selling of marijuana when compared to whites. Though the disparity in marijuana possession between African American/Blacks and whites was reduced slightly after legalization, the disparity for selling marijuana has more than doubled since legalization.

"Local trends

"While statewide studies have the ability to control for individual law enforcement agencies or police departments, monitoring trends in marijuana-related crimes within a local police department can provide details of violations that statewide data systems do not. For example, violations for public consumption of marijuana cannot be directly queried from state-derived data; however, local law enforcement agencies and municipal courts maintain details on the nature of the crime that would indicate whether someone was ticketed for public consumption vs. possession or a different drug-related charge. One example of the potential of local data to explore issues of criminal justice can be made using data from the Seattle Police Department (SPD). A 2015 report for the Seattle Community Police Commission showed a disproportionate number of citations for marijuana public consumption issued to African Americans/Blacks in Seattle.12 Using local police department data is key to understanding differences in the implementation and enforcement of polices pertaining to the legalization of marijuana."