I think the reason is because what someone who's on Veritaserum says won't necessarily be accurate; they will say what they remember and/or THINK is the truth, so they're not lying, but they could be mistaken about certain circumstances (and I think if they had been under the Imperious Curse, for example, their memory of what they did might be faulty).

An article from gamer rant said this and I agree.

Veritaserum, or the "Truth Potion," is a powerful potion that compels the drinker to speak the truth, but it is strictly regulated, and its use is limited by the Ministry of Magic.

The effectiveness of Veritaserum can be undermined by a skilled witch or wizard who can protect themselves with counter-spells or counter-potions. A person's perception of the truth can also influence their answers while under the potion's influence.

The limitations of Veritaserum make it an unreliable and imperfect method for determining guilt or innocence in criminal trials, as it can be resisted or manipulated, and it does not guarantee objective facts.

@Cabbage Man Fan is correct 💯

I think the reason is because what someone who's on Veritaserum says won't necessarily be accurate; they will say what they remember and/or THINK is the truth, so they're not lying, but they could be mistaken about certain circumstances (and I think if they had been under the Imperious Curse, for example, their memory of what they did might be faulty).

AND WHAT IF OBLIVIATE (ze memory-erasing spell for those who dont know) OR THE MEMORY-ALTERING SPELL THAT HERMY USED ON HER PARENTS WAS USED ON THE PERSON IN LE TRIAL- whomp whomp

I think it's like lie detectors, even if they can be accurate most of the time, you can't use them in trials, because what trials need is factual evidence.

^ Yes; veritaserum not being admissible in trials also reminded me of lie detectors. Someone might pass a lie detector test even if they aren't being truthful (much like where wizards can beat the test, as Cabbage Man Fan shared) and someone who is being truthful but is nervous, for example, might fail a lie detector test.

A skilled Occlumen can resist veritaserum. Barty Jr couldn't because he wasn't mentally focused.

Thank you. for sharing my opinion.

Okay! Thank you all!