Unlike cravings, urges can usually be suppressed by willpower.
Urges are less powerful than cravings. Urges are often passing and temporary.
Cognitive skills can be learned to effectively suppress urges.
Urges can usually be traced back to a source like stress, depression, anxiety, etc. which provides motivation for the escape or comfort of the substance, while cravings may have no external source and the person may have no idea why they are craving and may actually not want to take the drug at all. (see cravings)