Ultimately with the individual it's a matter of choice. However, studies have determined that individual is differentially at risk for engaging in drug-taking behavior. Factors that increase the probability of drug use are called risk factors; those that lower the probability of drug use are called protective factors. People with a high number of risk factors are said to be vulnerable to drug abuse or dependence, while those who have few risk factors and more protective factors are said to be resistant to drug abuse.