A survey by the Drug and Alcohol Foundation shows that nearly one in three families are affected by drug and alcohol problems.
Thirty-one percent of the 500 people questioned have had a family member whose substance abuse has negatively affected their lives.
Fifteen percent said they don't know who to ask for help if a family member is having problems with addiction.
Foundation director Ross Bell says for every person with a drug problem, four people around them are affected - but the stigma of drug and alcohol abuse makes it hard for people to seek help.
Mr Bell says he believes the real figure may be even higher, because many people do not like to talk about it.
"People who have problems or families who are experiencing problems feel the shame and the stigma of those issues," he says, "and they're afraid to put their hand up for help."