When absent for only a brief period of time, recipients of the pheromones experience withdrawals that intensify with time. Though not apparently fatal, the absence of the pheromones causes depression and possibly other mild forms of sickness. John Sheppard, who had a cold at the time he was introduced to Lavin, was unaffected by the pheromones. Though it is suspected that, with prolonged contact with Lucius, the pheromones would have won anyway.
Dr. Carson Beckett, while pulled away from Lucius long enough to clear his head, managed to devise an antidote which neutralizes these pheromones -- perhaps permanently.
Irresistible - Lucius explains his secret to Colonel Sheppard while he is behind bars -- a pheromone created from an herb found on only one planet in the galaxy.