If your cat reacts in a way that could endanger the cat or the groomer, medication may be needed. Ace is commonly prescribed. It is not a good choice. Many groomers will not groom a pet sedated with Ace. Why? The cat will be hypersensitive to noise, so the sound of clippers and the dryer could cause panic. The cat is aware of what is happening but unable to react in a logical way or understand the situation. That’s a recipe for panic. Cats can and do bite while on Ace. Not to mention the fact that it is unkind to put them in a situation in which they are fearful yet helpless.
This video by a veterinarian explains why.
Also, read the Feline Handling Guidelines in the Journal of Feline Medicine and Surgery 2011. They are against the use of ACE.