I started watching Teen Wolf after a friend suggested it to me. Here's what you need to know:
Season 1 is relatively safe. There's a LOT of violence. The first episode shows the body of a girl who had been torn in half. There's a flashback of a werewolf attack. There are various fighting scenes between werewolves and hunters. Werewolf attacks occur almost every episode. There are flashbacks to a fire, in which many people died. A girl's aunt has her throat slashed. A werewolf is set on fire, then has his throat sliced. There is also some swearing, though the worst thing they say is "$#it". Two main characters are in a romantic relationship (they kiss many times). A friend informs a girl to give a guy "a taste". A packaged condom is shown.
Season 2 gets more bizarre. A teen boy starts killing people. Two main characters have delusions. There's one disturbing scene in which a snake goes into a teen's mouth, then breaks through his eye (all of this is only in the teen's mind). It's shown that a boy had suffered abuse in the past (his father throws things at him and used to lock him in a box in their basement). Hunters cut werewolves in half in order to kill them. A werewolf comes back to life. A main character's mother commits suicide after she gets bit by a werewolf. Teens and adults are held captive. A teenager drowns. A grandfather is willing to kill his own children is order to be cured from cancer. There are also several sexual scenes. It is assumed that several main characters are sexually active. There is a flashback of two teenagers in bed together. A mothers asks a boy if he's sleeping with her daughter.
Season 3 continues to get worse. Several teenage characters die. There's a scene is which a man's head is crushed in. People start being killed for sacrifices. Each sacrifice is strangled, has their throat slit, and their head bashed it. A man has arrows stuck into his eyes. TONS OF VIOLENCE. Teens are poisoned so that they try to commit suicide. None of them succeed, but we hear and see creepy scenes of the voices trying to convince them to kill themselves. A boy almost drowns, and another almost lights himself on fire. A werewolf is impaled (though he doesn't die). There are more sexual scenes. One girl is very promiscuous; she's shown kissing several guys, we see a man in her bed, and she claims that she doesn't want a boyfriend, she wants a "distraction". Another girl says that she doesn't want to be a "seventeen year old virgin" anymore, and kisses a main character. They intend to sleep together, and the boy gets condoms, but the girl disappears. Two girls kiss. Two boys kiss. Adult characters make out on a bed. A teen boy walks into a bathroom while a girl's taking a shower and says it's okay, since he'd seen her naked before. It's suggested that a boy has a erection.
I wouldn't suggest the show for teens. I watched it much longer than I should have, because I hoped that it would get better as it went on. Sadly, it didn't. It's very gruesome, very sexual, and has very few role models.