I have a 6-1/2 pound poodle/bishon, he will not let the groomers groom him,he gets very aggressive, he even bit one of the groomer. I heard that I can give him benadryl to calm him down. Is that true ,how much to give him and what kind of Benadryl? I have Benadryl/Allergy.

However much the veterinarian says is safe. DO NOT give a dog a human medication without checking with a vet.

While it does have sedative properties, Benadryl won't work very well for your dog. I suggest speaking to your vet. They will determine the health of your dog and suggest something to help, like acepromazine tablets which are fairly common to use as sedation in dogs.

Benedryl is usually given for allergies or irritation but only after seeing a vet to determin dosage.

There are some ways you can prepare your dog for the groomers without having to give it drugs.

First and foremost I would suggest obedience training classes to help get your dog unde control and work on the aggression problem.

What we do with puppies before their first groom is just put them up on our dining room table and get them to stand there.
Hold the dog under the chin with your thumb on one side of its neck and your fingers on the other, pull up slightly so the dogs head is help up.
This is usually how groomers hold dogs so you want to get him used to standing in this pose.

Once he is comfortable doing that (it might take a few 'sissions') hold him in the pose and get a brush, just gently give his coat a brush. If he behaves, put him down and give him a treat.
Increase the brushing time until he is comfortable doing it.

Next it's back on the table for scissor work. Hold him in the pose again and grab a pair of scissors. You don't have to actually cut his coat but just open and close the scissors near him to get him used to the sound.

Next... clippers.
This one can be hard but if you have anything that vibrates (a mobile phone, electric razor etc) it will work.
Again, hold the dog in the pose and just touch the vibrating object on him. Only for a short period at first and gradually build it up until you are running the object over the dogs body.

Lastly, the dryer.
Get a hand dryer and flick it on (dog in pose on table again) and just hold it away from him. This is only to get him used to the noise.
Gradually work up to having the air on the dog, and finally moving over the dogs body (don't foget to use the 'cool' setting)

Nail cutting: You will need a pair of nail clippers for this even if you don't use them.
Just hold the dog and grab one of his paws. Separate a nail out and hold it. Get the nail clippers and just get them to make the SHOONK noise against the dogs nail.
Repeat for each nail.

I think that covers most things a groomer does.