How do the experts make the distinction between mild substance 'Abuse' and more severe substance 'Dependence'? The answer depends largely on whether or not the addicted person experiences Tolerance and Withdrawal.
Tolerance is the name given to the case when, over time, a drug or alcohol user requires more and more substance to get the same amount of 'high' effect they are seeking. Typically, the more a person takes drugs or alcohol, the more that he or she will become tolerant to its effects, requiring more and more of the substance to get the same effect. Tolerance, then, is what is happening when someone starts needing to drink six drinks to get the same 'buzz' that they used to get by only drinking three drinks.
Withdrawal is the name given to the negative experiences and cravings that a drug or alcohol user may have when they stop taking using drugs or alcohol. For example, an alcoholic who stops drinking abruptly may experience one or more of the following negative symptoms: anxiety, sweating, increased heart rate, hand tremor, insomnia, vomiting, agitation, hallucinations, and even seizures. A drug or alcohol user in withdrawal becomes highly motivated to get and take more drugs or alcohol, as this relieves their feelings of sickness. As one might figure, an alcoholic who experiences such an array of negative symptoms even once, will be highly motivated to remain drunk so as to avoid ever having to experience them again.
A person must be experiencing significant social, relationship, family and/or occupational difficulty due to their substance use in order to qualify for a Substance Abuse diagnosis, but they need not have ever experienced Tolerance or Withdrawal. A diagnosis of Substance Dependence, however, cannot be made if Tolerance or Withdrawal is not present.