the-art – Actually there is no single scientific definition of addiction. Excessive use despite the consequences is one criterion used to determine if a substance or behaviour is addictive but there are others, including craving the substance or behaviour in its absence, whether tolerance levels increase over time (i.e. increasingly greater amounts of the substance/behaviour are needed to get the same level of ‘high’ as previously experienced) and whether physical withdrawal symptoms are displayed after sudden, prolonged cessation of the performance of the activity (this is different to craving which is purely an extreme, overwhelming desire to re-experience the ‘high’; withdrawal symptoms are physical, including nausea, excessive sweating, cramps, loss of concentration etc.).
lakewood001 – Addictions are always physical. Some things which are often described as addictive (such as the internet, video games etc.) are not physical and, as such, are not classed as addictions by the DSM. Behaviours which are addictive include overeating, gambling etc. and do have actual neurobiological facets.
JustARegularJew – Interesting point. There is much discussion in the world of addiction research as to whether or not this is the case. The evidence is inconclusive but the DSM does currently go with this distinction between addictive behaviours and addictive substances.