My vet insists not, but I have been giving Stronghold flea drops to my cat for seven years. For the past 6 months she has had fleas, and it's very annoying for her (and me when she sleeps on my bed and has frenzied bouts of grooming all night.)
The vet says it doesn't matter because the fleas will bite her and die, but in that case she's finding an inexhaustible supply of them from somewhere! She does sit in the garden a lot, but she always has, and the poor thing is being driven to distraction.
Is anyone else having a similar problem?