Alcoholism was an addiction to alcohol.
One effect of alcoholism was memory loss. When Nina Rogers had her memories stolen by a sentient book she and her housemate believed it was a result of her excessive drinking. (PROSE: Consequences)
George Wilson was an alcoholic and blamed it for his and Lorraine's divorce. Kate said that both topics were off-limits to Jack Harkness during his interview. (AUDIO: The Conspiracy)
Tommy Pierce was a recovering alcoholic and was assisted by Pippa, although he did occasionally relapse and end up staying at Torchwood Tower later than usual. After Rachel Allan framed him, spiked his coffee and had him fired, Yvonne Hartman arranged for him to receive help for his addiction. He did not drink a drop after being fired. (AUDIO: New Girl)