psychological dependence is a biologically based craving for a specific drug
Physical dependence on drugs is marked by growing tolerance of a drug's effects, so that increased amounts of the drug are needed to obtain the desired effect, and by the onset of withdrawal symptoms over periods of prolonged abstinence.hysical dependence on drugs is marked by growing tolerance of a drug's effects, so that increased amounts of the drug are needed to obtain the desired effect, and by the onset of withdrawal symptoms over periods of prolonged abstinence.