The city where Democrats are holding their national convention has become a 'mecca' for heroin users

The Democratic Party will meet in Philadelphia this week for its national convention amid an increasingly contentious political environment.

But the convention will also take place against the backdrop of a more sinister American phenomenon: Philadelphia has become a hub for the heroin epidemic that has swept the US.

Philadelphia has seen an influx of hundreds of heroin addicts in search of a cheap, highly potent version of the drug reportedly pushed by Mexico's powerful Sinaloa cartel, according to the Los Angeles Times.

"The purity is the best on the East Coast, and it's easily accessible," Patrick Trainor, spokesman for the US Drug Enforcement Agency in Philadelphia, told the LA Times. "It definitely draws people."

Justin Smith, a 32-year-old addict who sleeps on a dingy mattress in a roadway tunnel, agreed with that assessment, telling the LA Times that the city had become a "mecca" for addicts from other parts of the country.

The neighborhood of Kensington, in northeast Philadelphia, has been described by experienced narcotics officers as one of the "most flagrant open-air drug markets" on the eastern seaboard, the LA Times notes.

In addition to being centrally located among the Mid-Atlantic's heroin markets, Philadelphia, and Kensington in particular, is adjacent to Interstate 95, a major artery for illegal drugs smuggled up and down the East Coast.

For much of the 1980s and 1990s, most of the heroin seized in the US, especially on the East Coast, came from parts of Asia.

Over the last 20 years, however, groups in Mexico - which now produces 2% of the world's opium, the base material for heroin - have made a concerted effort to push into the US heroin market, with the Sinaloa cartel of currently jailed kingpin Joaquín "El Chapo" Guzmán likely leading the way.

Over that same period, a shift toward prescribing opioid painkillers, and a subsequent crackdown on the overprescription of such drugs, has driven many Americans toward a cheaper, more powerful high - often relying on heroin for it.

Those Mexican suppliers, the LA Times notes, started supplying cheaper, more pure heroin to big US cities like New York and Philadelphia. By 2014, 80% of the heroin seized in Philadelphia was of Mexican origin.

In June, DEA agents in Philadelphia seized heroin that was 92% pure, which Trainor, the DEA's spokesman in the city, told the LA Times was twice the purity of what would've been seized a decade ago.

Heroin use throughout the US has skyrocketed. The UN's World Drug Report 2016 put the number of heroin users in the US in 2014 at about a million, nearly three times as many as in 2003.

Guzmán's cartel is believed to control much of the US drug market and is the major player in Mexico's Golden Triangle, which includes parts of Sinaloa, Chihuahua, and Durango states and is so named because of its extensive drug cultivation.

The Sinaloa cartel is also thought to have a significant presence in Guerrero state, Mexico's other major heroin-producing region, but with the proliferation of criminal organizations in that state, and the intense bloodshed that has resulted from their clashes, it's likely that multiple groups are involved in Mexico's heroin trade.

Though Mexican suppliers may be fragmented, they remain responsive to market demand. "The heroin supply chain appears to be a largely horizontal, diversified operation with multiple actors, and one that is obedient to market forces rather than one or two single vertically integrated distributors," Steven Dudley, codirector of InSight Crime, said in testimony before the US Senate Foreign Relations Committee.

By and large, these Mexican groups rely on criminal networks within the US for street-level distribution. Guzmán himself has been recorded haggling with Chicago-based distributors, and his Sinaloa cartel reportedly relies on gangs like MS-13, the Latin Kings, the Crips, and the Bloods to distribute drugs in other US cities.

'They ain't gonna do nothing for us'

While who controls Mexico's heroin market is murky, seizures at the US border are up 40% between 2009 and 2015, according to the Customs and Border Protection agency.

And while it's not clear how much opium production has increased in Mexico, some US and Mexican officials estimate it grew by 50% in 2014 alone.

Mexico is known mainly for production of low-quality, "black tar" heroin, which has traditionally been found west of the Mississippi River.

But Mexico's heroin producers are suspected of copying South American heroin-production methods to reproduce the higher quality "white powder" heroin made by South American producers, generally Colombians, with the likely goal of challenging those producers' control of eastern US heroin markets.

As of 2012, the DEA reported that Colombians supplied a little more than 50% of the heroin in the US; the Mexicans supplied about 45%.

Heroin-related deaths have increased five-fold since 2000, with drug-related deaths that involved heroin increasing 244% between 2007 and 2013 alone.

Of Philadelphia's 720 drug-overdose deaths in 2015, which were a 10% increase over the previous year, about one-quarter involved heroin.

Many heroin-related fatalities have been blamed on the addition of fentanyl, a potent painkiller that can be 50 times stronger than heroin and 100 times stronger than morphine, according to the US Centers for Disease Control and Prevention.

Dealers sometimes add fentanyl to heroin in order to product a more powerful high, but even small doses of the additive can be lethal.

Seizures of fentanyl, which has been linked to Prince's death earlier this year, jumped from 618 in 2012 to 4,585 in 2014.

Caught up in America's unfolding heroin nightmare, many of the users in Philadelphia are unmoved by the Democratic National Convention, which starts on Monday and will take place only about 7 miles from the Kensington neighborhood.

"They ain't gonna do nothing for us," a 44-year-old addict who had gotten a job cleaning hotel carpets ahead of the convention to finance his habit, told the LA Times.

"I can't worry about America when I can't even worry about [living under] this bridge," the girlfriend of another addict said.