His relationships would likely be strained. Since he can't control what he says, he might say things that hurt his friends' feelings. For example, he could blurt out that he thought Ron's Quidditch skills weren't as good as he pretended. This would surely cause some friction between them.
It could start with someone having a malicious intent towards Harry. They might slip him the Veritaserum in a drink or some other way. Then, as he starts to spill the truth, it creates a chain reaction. People around him start to react to the things he reveals. Maybe his friends try to protect him from further exposure, while his enemies try to get more information out of him.
Well, if Harry is given too much Veritaserum in this fanfic, he might start revealing all kinds of secrets. He could disclose things about his friends that he wouldn't normally tell, like Hermione's insecurities or Ron's hidden fears. It could also lead to him accidentally spilling information about the Order of the Phoenix's plans, which would put everyone in danger.
Well, if Harry is given too much Veritaserum in fanfic, one consequence could be that he loses control over his own narrative. Since Veritaserum forces you to tell the truth, he may end up sharing things that are not only personal but also strategic in the fight against Voldemort or other enemies. This could disrupt plans and alliances. Also, it might change the relationships around him. His friends might be shocked or disappointed by some of the things he reveals, and his enemies might gain an upper hand. It could lead to a very different storyline compared to the original plot.
Well, in a fanfic, if Harry is given Veritaserum, he might reveal all kinds of secrets. Maybe he'd spill the beans about his true feelings for his friends, like how much he really trusts Hermione and Ron. He could also disclose some hidden details about his battles with Voldemort, things that he's kept to himself because of fear or just not having the right moment to share.
There are some fanfics out there where Harry is given Veritaserum. Some of them focus on the comical aspect of it. For example, Harry might accidentally drink Veritaserum at a party and start blurting out funny things about his classmates. Others might take a more serious turn and use it as a plot device to uncover a mystery or a conspiracy within the wizarding world.
Harry might initially be shocked and try to resist. But since Veritaserum is powerful, he would soon start answering truthfully. He could look angry towards Snape for using such a potion on him without his consent.
After Umbridge uses Veritaserum on Harry in a fanfic, the plot could develop in various ways. If Harry reveals secrets about the resistance against Umbridge, she could crush it. On the other hand, his friends might try to rescue him from the situation and that could start a whole new adventure of escaping Umbridge's clutches.
Dumbledore, if he finds out, would surely take action. He might not be able to reverse the effects of the Veritaserum immediately, but he would find a way to protect Harry from any long - term consequences. The other members of Dumbledore's Army would be in shock. They would worry about what Harry has revealed and also feel a sense of guilt for not being able to protect him from Umbridge's devious plan. Some of the more rebellious students might even start a protest against Umbridge's use of Veritaserum on a fellow student without proper authorization.
It may slow down the plot. With too much time, the pacing could be affected, making the story seem less urgent at first. For example, if Jack Reacher is waiting for something, this excess time can build suspense.
Well, if Umbridge uses Veritaserum on Harry in a fanfic, it depends on how the author writes it. Some fanfic writers might have Harry spill out information about the Order of the Phoenix, which could put the whole organization at risk. Or perhaps he'd talk about his experiences with Voldemort that he's been keeping to himself. This could potentially change the whole dynamic between the characters in the fanfic, especially if Umbridge uses this information to her advantage.