There are plenty of options for calming cats without a prescription for their grooming experience, such as calming treats (Pet honesty makes a very palatable treat for calming cats),
Sometimes a prescription for gabapentine is necessary to take the edge off in order to groom a nervious or anxious cat safely, to prevent the cat from trying to squirm and kick its way out of the grooming process. Often times this is all that is needed (the so called magic bullet) to get the job done.
However, some cats continue to growl, hiss, bite and claw their way out of the grooming experience even with medication. Safety is alway top priority for the cat and anyone handling it so that no one gets hurt during the grooming process.
Thrusting about increases the chace of injury to the cat from the grooming tools which could require an emergency trip to the vet for stitches and or antibiotics. Also if the people handling the cat get bit this can also warrant a trip to the E.R. A catbite is a puncture wound often requiring a tetanus shot and antibiotics. I personally know of one groomer who had to be hospitalized for three day with I.V. antibiotics from a cat bite.
Sometimes the only option is to have the cat anesthetized by a veterinarian to get the job done safely.