Does anybody know side effects for flea drops. Two days ago I put flea drops on my 3 month old puppy and now she will not eat. Drinks water but throws it up. She has not energy.

Is that the king you put on the back of the neck?

Yes you put it on there back.

Much of that is going to depend on what exactly you used. Some animals can have a sensitivity to these products. Usually cats but dogs can be affected. Do you still have the box?

Pet Poison Helpline - 24/7 Animal Poison Control Center (http://www.petpoisonhelpline.com/)

Call this number and give them the information they need.
This could be something other than the treatment, depending on vaccines and deworming, etc. Could be a number of things.
You can bathe him in Dawn dish soap to wash off the remaining product to be on the safe side. Make sure he doesn't get chilled.
But you will still need to get him to the vet to be checked.

Hartz ultra guard flea and tick drops with phenothrin 85.7% side effects salivation, tremors, loss of appetite, weakness. And vomiting. My 3 month old puppy is very sick with these side effects. Do not buy this product.

Get him to the vet sooner rather than later.

If what is going on is due to this he will need vet care immediately. Works on the nervous system so don't waste time.
Good Luck I wish him well.