I've heard you can use phenergan as a sedative for dogs, what dosage should I give a dog that weighs 34kgs. She's started freaking out during storms.

I'm not familiar with this drug, but never give a dog anything that's a human preparation without checking with a vet first - rule of thumb. And in fact in cases like this it's far better if you don't dull her senses as it could make her more worried than she would be. If this is something new, I think you need to have her in for a health check.

Isn't Pheregan used for nausea and vomiting,a family member used to take this when he was going through cancer treatments.

I dont know how this would be used as a sedative.