Instruct: Classify Amazon reviews into positive or negative sentiment
Query: stops working

I would caution against using this product for more than a few months because it stops working. I had been using it on my 3 cats and noticed that after about 15 days, the fleas would return in full force. I did some research online which showed many other reports of Frontline no longer working, and when I called the vet they also suggested we move on to another product.