Author's note: Please keep an open mind. I've been an addict for serveral years and I know the Remus in my fanfiction is not like the one of JKR ;)
The drugs had been something Remus Lupin had been having trouble with ever since James and Lilly died. That's when everything went wrong. In just two weeks his whole life had been turned upside down. He lost his mother first… she had taken an heroin overdose. Next he lost James, Lilly and Harry. Not long after that he also lost Sirius and Peter. He filed for custody of Harry. The battle was long and hard. In the end it was all the same. Werewolves were not permitted to take care of children. Remus couldn't go to collage anymore, because Sirius paid for everything. He got kicked out of the appartment too, where he used to live with Sirius.
Homeless, poor and without any family or friends left Remus sank into a deep depression. He stopped eating. Didn't get out of bed anymore. And the Order of the Phoenix was to busy celibrating the first war was over to notice Remus had ended up all alone.
In his last attempt to keep his head above water Remus went to see a psygiatrist. He got presctiptions and he took them like he was told to. But they just didn't work. Nothing took away the pain. The loneliness. Nothing.
By now he was living in a small and dirty hole that you could hardly call an appartment. One day his neighbour said: 'Hey, I have something that would help against the pain.' And Remus went with him. The other man offered him herion and he took it without any further thought. Finally he found something that worked. He was happy again.
It was difficult to support his happiness tough… he started selling his blood at the black market. Werewolf blood was worth a lot of money. And then he had to move into an even smaller appartment in order to keep taking his beloved drugs. In the years after that there were serveral times he quit. He got clean and went looking for a job. But then something shit happened and it seemed like he had no controll over himself whatsoever. He fled to his drug again and again.
Finally Dumbledore found out. He told Remus to wean himself off and come to Hogwarts to teach. Start his life over again. And Remus did. And everything seemed to go into the right direction again. He got reunited with Sirius and rejoined the Order immideatly when he heard the word. He met Tonks and it was love at first sight.
One day he was singing in the shower and Sirius asked him what he was so damn pleased about. Remus thought it was time. Time to tell Sirius he was in love with his little cousin.
Sirius didn't take that news very well. He got very angry. Screamed at Remus and called him names. Told him she was out of his reach anyway. Sirius died a couple days after that.
Remus was glad his friend never knew he had become a junkie. An addict, just like his mom. His arms were covered in track marks. Sirius never asked about them and Remus never told him. As always Remus was back on the streets again. Looking for a dealer who sold the strongest stuff. His drug of choise. Herion. Sometimes he didn't even had to pay for the drugs, the fact that he was a wolf frightened the dealers so much he could threaten them into giving it to him for free.
Tonks became his rock. She was so upset that Sirius passed away. They spent more and more time together. And one night she caught him.
Remus had expected her to be at work all night, just like she had told him. So he got into his bed with a syringe, a phial and a tourniquet. He fixed himself up and lay down, enyoing the rush. When he got down from his high he passed out from the sheer exhastion of it all. One hour later he opened his eyes and shot up a second time in a row. That's when Tonks came into his room for one of their midnight sessions. She got off work early.
To be continued… (reviews would keep me going haha)
Author's note: Because Remus is a werewolf, there is no one who would hire him. So he kept un studying in dire hopes of creating a better carreer perspective for himself. I can imagine him going to a good university in order to get his Master degree in litterature or Dark Arts or something :)