What makes the difference between a casual drink and alcohol dependence? How do you know when someone goes from trying marijuana now and then to having a serious abuse problem? Scientists still do not know how all of the factors involved in substance abuse work together, but a series of studies provides insight into how age plays a factor in going from using a substance to abusing it. Three studies provide related information with a glimpse at the patterns of drug abuse. In 1994, Anthony, Warner and Kessler provided information showing probabilities for drug use and drug dependence. A 2002 study by Wagner and Anthony compared the time difference between a first experimentation with a drug or alcohol and the progression to drug dependence. In 2007 Wagner & Anthony explored the gender differences in these patterns. All three studies used data from the National Comorbidity Survey (NCS) from 1990-1992. The studies collected data obtained from 8.098 participants between the ages of 15 and 54. The researchers used a collection of data from 6,792 participants between the ages of 15 and 54. During the NCS, the participants were interviewed in person using DSM-III-R criteria for dependence on alcohol, marijuana and cocaine. Comparing each individual drug, the data was compiled to show the age at first use of the drug and the age at which the onset of drug dependence was established. Out of the 8.098 participants total, 7.485 of them were alcohol users, 3,940 were marijuana users and 1,337 were cocaine users. 15-16% of participants who used alcohol once ended up developing a dependence on alcohol, while the rate was 16-17% for cocaine users and 9% for marijuana users. The first use of each drug peaked at age 18 for alcohol and marijuana, while cocaine showed a later age of 20 for initiation. The risks of a first use progressing to a dependence also followed a similar pattern, with a peak during teen years for alcohol and marijuana, and a later age of 23 to 25 for cocaine users. The risk of becoming dependent on cocaine was intense and continued to be a high probability for about the first decade. Alcohol and marijuana patterns were not as immediately following the first use. The risk of developing alcohol dependence, however, was lasting for decades. There were some gender differences observed, but only for marijuana dependency and not cocaine or alcohol. Male marijuana users were about twice as likely as females to become dependent within the first 2 to 5 years of initial experimentation. This series of studies confirms earlier research showing that the likelihood of a first use of alcohol, marijuana and cocaine is highest before the age of 25. The research provides information that promotes education and intervention with those under the age of 25, specifically focusing on the risk of dependence for those tempted to try a substance for the first time.