Hans has two rules for himself: Before he gets high, he needs to make sure his Labrador has enough food for a day, and while he is high, he's got to "not get on other people's nerves." Hans is homeless, has pancreatic cancer in the terminal stage, and doesn't give himself "more than a year." Next to him sits Robert, his hunched back bending toward the right. HIV gives Robert just as short a life expectancy as Hans. I met both of them in Frankfurt's Taunusanlage train station; in the 1980s this place would be packed with several hundred heroin addicts shooting up. Today, Hans and Robert can smoke crack in peace.

The pipe sizzles when Hans ignites his butane lighter, and then the air smells disgustingly sweet, like burnt plastic and ammonia. "I've already smoked three times since this morning," he says.

Most of the users who hang out in Frankfurt's Bahnhofsviertel neighborhood rarely make the trip to Taunusanlage, even though it's only feet away. The craving for crack can at times get so consuming, they just light up on the street immediately after buying it—huddled against buildings, between cars, or in shop entrances. The ones who can't afford to score hold out hope for some charity, biting their nails and clenching their jaws.

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In Germany, crack is a rather rare drug. Even though the 1980s tabloid press warned that the "deadly drug" was about to wash over the country like a flood, crack hardly spread beyond Frankfurt. According to a national report on narcotics, Hessen, the state that Frankfurt belongs to, is Germany's absolute forerunner in first-time crack users—217 people registered there in 2013. Hamburg follows in second place with a mere 17.

The drug has probably taken hold in Frankfurt because the city is geographically central and people fly here from all over the world. There's also been an open and visible drug scene for a long time in the Bahnhofsviertel, where crack use spread in the late 1990s. Cocaine in powder form has rarely been sold on the street since then. Meanwhile, crack's popularity has been rising continuously for years.

More than half of the addicts in this neighborhood consume a mixture of cocaine, baking powder, and chemical fillers, according to local police. It outsells heroin, while 97 percent of the drug addicts in the district have had experiences with crack. It's now the number-one drug consumed by addicts, with two dying last year from an overdose of crack mixed with other drugs.

In the Bahnhofsviertel, the "rocks" are having a devastating effect on users. No other drug is quite so addictive or as voraciously consumed. Few other substances take such a toll on the body, while faces also become gaunt and skeletal.

Many feel the drug is poisoning the entire neighborhood, while the reports of instances of aggression are frequent. A lot of residents, however, don't want to speak openly, fearing retribution from drug dealers. The dealers operate on shopping streets and threaten business owners; they stash their product in hourly hotels, dodgy cafés, and abandoned buildings. Addiction is also causing a rise in petty crime, even forcing some in the neighborhood to turn to the Hells Angles for protection.

The crack trade is really booming on Taunusstrasse street. At peak times—between six and eight in the morning—there's a dealer posted every few feet, offering their services to any passerby. If the police pick any of them up, a replacement will quickly take their place. North African and Albanian gangs dominate the trade and fights inevitably break out, often resulting in stabbings. "Hey, man, what's up, you need anything?"—at certain hours of the day, you'll hear this repeatedly while walking down a short stretch of Taunusstrasse.