This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / 21 Jump Street
The episode I'm Ok, You Need Work—Hanson finds out that the kid he rescued in the Pilot episode has been thrown into a corrupt institution posing as a drug rehab center. When Hanson goes to rescue the kid, he finds the institute to be a hell hole where the patients are routinely abused by the guards and the staff, and doped up to make them seem like hopeless addicts. To top it off, they are only officially "cured" when the parents of said children's health insurance dries out. Tom, like his friend before him, gets abused, doped, restrained and transferred to a mental institution to silence him from testifying. To add insult to injury, that same kid died while trying to escape from a vent shaft. To make matters worse, the institution staff refuse to believe Tom is an undercover cop, which gets him into more trouble. When Hoffs and Fuller manage to find him he is barely alive, and dazed.
The real Nightmare Fuel is that these rip-offs / abusers posing as "institutions" exist in real life - this stuff (like all of the problems this series adressed, actually) was not made up for the series but comes from real life...
Loc'd Out / Draw the Line in which Hanson, even though innocent, is wrongly convicted for a murder and ends up in prison. Extra harsh if you're a cop yourself. To make it worse, turns out the person who deliberately set him up and lied in court to get Hanson convicted, is a (corrupt) police officer himself.
Also in the aftermath of aforementioned episodes: Ioki is almost mortally wounded in those, spending some time in a coma. After he wakes up and goes through physical rehabilitation, he is still haunted by flashbacks (in an PTSD manner) of him getting shot, and gets addicted to pain-killers.
When you re-watch this show, decades after it was made... it's absolutely terrifying how many controversial issues it raised are every bit as relevant today (poverty; domestic abuse; racial tensions; teenage pregnancy and STD's and abortions and controversy over abortion; book burning and religious hatred; hatred and abuse of gay people; corruption within the police force, military force, and municipality, etc.; even war and its devastating consequences (in the series portrayed by the Vietnam war and by the El Salvadorian war, but keep in mind that after this series the Gulf war and war in Afghanistan, amongst others, happened...)).