"So, you have a patient then, Slave?" - Protagonist
The Hospital Harem is one of multiple routes in Adventure High.
In it, the Protagonist has enslaved Dr. Tiff and is using her to enslave the other students in the school that comes to the hospital for healing.
Note that this is just a general outline for the route. It is not a walkthrough.
The First Slave
To access this route, the Protagonist must either start the Redemption Route and then get help from Ms. Rack to enslave Dr. Tiff.
Once done, speak to Dr. Tiff again and at first, talk about Ms. Rack. Realizing that this is probably not the safest option, choose to talk about something fun the next chance you have. Dr. Tiff will agree to help you enslave any student that comes there.
Otherwise, if the Protagonist gave Ms. Rack the book at the end of any of her Secret Classes, simply tell her to share it and then head to Dr. Tiff's room. In that scene, tell her to help you enslave any student that comes.
Note that you must have reached floors thirteen and fourteen of the dungeon for the first two scenes to play out - there is no upper limit, so reaching floor fifteen for the Sigil still makes you able to start those scenes.
After you've done that, just enter Dr. Tiff's room - there's a 1/4th (25%) chance that a scene will trigger, in which she will enslave a female student that entered.
Slave Number Two
At any point after this scene, enter the room and another scene might trigger in which the Protagonist gets the option to either enslave a nameless NPC or simply cure her and let her leave again.
Should the Protagonist enslave her, she'll be told to bring more people to Dr. Tiff's room to get enslaved, which she obeys to doing.
Monster Girl Slave
After seeing the second scene, the Protagonist needs to have access to the Stone Skin spell and have reached floor 18 of the dungeon. At random when entering (seemingly a 25% chance), a student will come in. She's been wounded by a slime and her body is transforming into one.
The Protagonist can either fix her simply by letting the scene play out, or during the line "...Alright. Here goes..." use a Chakram om her, turning her into a slime girl and the Protagonist's new slave pet.
An Enhanced Slave
(Note: This one requires you to have seen the Bimbo Teacher scene in which she appears first).
The Protagonist meets with Dr. Tiff again, who this time is greeted by a student who needs help.
The student have two, literally, giant issues: her breasts won't stop growing.
The Protagonist is given two options - either enslave the girl or have Dr. Tiff fix it. In case she gets enslaved, she reveals she just wanted bigger breasts to look more like Dr. Tiff, who thinks it's a compliment, but is unsure.
This is all that exists on this route as of version 0.62.