Don't ever give your pet any medication meant for people without your vet's okay. This is highly dangerous. How would you even know your dog needed a muscle relaxer? I hope you forget it. It's a really bad idea.
Can You Give Muscle Relaxers To Dogs?
No Not Really Because It Doesn't Really Work For For Dogs
There are many human medicines that are poisonous to dogs. If your dog is becoming aggressive then you may want to look at dog obedience training instead of sedation. Find out what is causing the aggression so your dog does not wind up attacking you or someone else. You certainly don't want to become afraid of your own dog. Obedience training can help before things get worse.