A flea treatment only works if the pipette is emptied onto skin the right size of dog is carrying, which is the reason spot-ons come in more than one size at all.

Johnson's Guardian Plus is a triple-action spot-on: applied from a single pipette, it's designed to kill fleas, ticks and lice on contact and stop flea eggs and larvae developing, breaking the flea life cycle both on the dog and, Johnson's say, in the home around it. This page covers the Small, Medium and Large dog versions; the pack we hold full label data for is the Large, banded for dogs of 20kg to 40kg.

• Triple-action: kills fleas, ticks and lice on contact
• Also targets flea eggs and larvae, to break the flea life cycle
• One spot-on pipette per treatment
• Large pack: for dogs 20kg-40kg
• Available in Small, Medium and Large dog sizes
• Johnson's recommend pairing with their Home Flea Spray for the house itself

On sizing. We only hold the full label detail for the Large pack, banded for dogs between 20kg and 40kg. The Small and Medium versions are sized for lighter dogs, but their specific weight bands weren't supplied to us — check the box for the exact range before treating a smaller dog.

Who it's for: dog owners running a routine flea, tick and lice programme who want a size matched to their dog's weight rather than a one-size product.