I wouldn't actually give the dog anything drug-wise. You'd probably get better long term results by getting to the root of the anxiety & sorting that out.
As I don't know you or the dog it's difficult to advise..but I'll try.
You could employ several friends to help you with this one...preferably ones that your dog has never met. Firstly put your dog in the main room & get the friends to come to the front door (probably 1 at a time to start with), they come in quietly, sit down avoiding eye contact with the dog, chat to you with the minimum of fuss & not too much movement. After a few minutes, they throw small bits of your dogs favourite food onto the floor near him, all the time with no eye contact. They then leave & a few minutes later, another person comes & you repeat the whole thing over & over..for about 30 minutes.
Several sessions of this training usually helps dogs with issues to do with visitors.
Don't allow the dog to go to the door to greet anyone...the idea being that YOU are the leader of the pack & YOU say who comes & goes in your home. In time, your dog should be able to feel he can trust you to take charge & he can take a back seat & not worry about visitors,because they are nice & not threatening. Do NOT let anyone who comes into your home make a fuss of the dog, they should be told to ignore the dog & if it approaches not to make eye contact...just calmly let him sniff them & then go away.
People tend to go a bit over the top with the fussing when it's a cute little dog & sometimes it can be a bit overwhelming when you're that small! This might be suitable for your dog, but you know your dog best.
Good luck!