I need some more information?
What kind of dog do you have? How much does he/she weigh?
Why do you want to give lorazepam?
Lorazepam is used sometimes for anxiety disorders in dogs, but the dose we use isn't high enough to sedate them. Plus the dose range is pretty wide... for a puppy that size he could take anywhere from 0.5mg to 2mg. Without examining him or knowing about any other medications he might be on, I can't recommend that you give it.
Puppies are wild. They need a lot of exercise and then they still seem to have too much energy. I would encourage you to look into as many interactive toys as you can.. Kongs stuffed with treats, buster cubes and treat balls, nylabones, etc. While I understand the temptation of using a sedative, it's just not a good idea.
Hang in there! and remember, he will grow up!