What makes a person abuse drugs? Some people never use drugs, even if drugs are easy for them to obtain. Others use drugs occasionally or regularly for years but never become dependent. And some people become addicted and unable to function without drugs. These differences in drug-use patterns are the result of a combination of environmental and genetic factors. Genetic factors refers to a person's genes, which are passed down from parent to child and are shared in part by other family members. Environmental factors include a person's experiences in the family, home, neighborhood, school, work, and other settings.