According to Louis Granger, he isn't a very good doctor and probably wouldn't be able to diagnose himself. Considering that he is also an alcoholic, it can be assumed that Gallagher is either a quack or lacks the qualifications needed to have a practice anywhere except for a lawless town like Thieves' Landing.
According to gossip overheard at the Pacific Union Railroad Camp, Gallagher also claims to have taken part in a big game hunt at Bearclaw Camp. However, the gossiper admits to being hesitant to believe such a dubious claim.
Aside from selling medicinal items to the player, Gallagher can routinely be found at the blackjack table in the Thieves' Landing saloon, wandering around town drunk, or gossiping about his patients and various other events. He may also be found hunting a boar or bear in a random encounter in the Tall Trees region of West Elizabeth.
You know that old-timer done shit himself again?
—Francis Gallagher, a subject with which Gallagher seems to have some fascination, as he continually brings it up during Blackjack games