After Christiane meets two friends inside of the Zoo station building, all three leave through a door looking for Detlef (Christiane's boyfriend) where the male prostitutes stand in line. One of her friends (Axel) wears flares-type light blue jeans inside the station, but outside he suddenly wears slim-fit dark blue jeans.
Christiane F. plays the David Bowie album, "ChangesOneBowie,"
in her room. But the song that is heard - the German version of "Heroes" ("Helden") - is not on that particular record.
Like many other movies, this movie exaggerates the physical withdrawal symptoms from heroin, which is not the biggest problem with heroin. (Other drugs can be much worse in this aspect, e.g. alcohol or benzodiazepine, people actually die when quitting those).
The psychological dependence is the main problem with opiates, as you can see when they start again after the withdrawal. This is very well depicted in the movie.
Some people never get rid of it.
When Detlef and Christiane find out that one of their friends has died, she looks in shock at the body. The next shot is a close-up of his arm and belly, but you can see his belly move up and down: he is breathing.
Christiane sees Detlev giving something to a girl from quite a distance. Then she is is very sure about him taking Heroine just for this action. It is never explained how she could be so sure about this in this moment. It could be any drug.
Before the concert, Leiche tells Christiane he is in bad condition because of a blood donation.
Then she looks for Valium (Diacepam) and gives him Mandrax (Methqualon). Both drugs are strong downers and would worsen his condition a lot.
It may be that he lied and she knows about it, but it's still very dangerous.