University of California at San Francisco researchers say they've genetically engineered mice that can receive morphine on a regular basis without developing tolerance or physical dependence. They believe the success of their genetic manipulation may point the way to developing a strong painkiller that patients can take over an extended period without increasing the dose to maintain effectiveness or worrying about withdrawal symptoms. Those certainly would be welcome improvements for patients in pain, but it would not, contrary to the UCSF press release about the research, "block dependency" or eliminate the possibility of addiction.
Both the university press office and the researchers themselves seem to be equating addiction with tolerance (the need for escalating doses to achieve the same effect) and physical dependence (the adaptation that results in withdrawal symptoms when a drug is suddenly withdrawn). Anyone who takes narcotics long enough and regularly enough will develop tolerance and physical dependence, but addiction requires a persistent desire to use the drug for its psychoactive effects. According to the American Psychiatric Association, tolerance and withdrawal are neither necessary nor sufficient for a diagnosis of drug dependence, and this is one of the rare occasions when I agree with the APA.
Otherwise, we'd have to say that everyone who regularly uses narcotics for pain becomes addicted to them, even though only a small percentage end up using such drugs for nonmedical reasons. We'd also have to go back to saying that drugs such as nicotine and cocaine (use of which does not lead to the clear, predictable tolerance and withdrawal associated with narcotics) are not truly addictive but merely habit-forming, a distinction without a difference. And if addiction were defined as tolerance plus withdrawal, it would not be meaningful to speak of addiction to things other than drugs that provide pleasure or relieve stress, such as gambling, sex, or shopping. Addiction is a pattern of behavior, not a chemical reaction; in the case of drugs, it resides in the person's relationship with the substance, not the substance itself.
Still, it's true that you don't often hear of addiction to aspirin or ibuprofen. If a drug company could produce a painkiller as strong as morphine that had no psychoactive effects, it would not be attractive to people seeking to get high or soothe their unhappiness. Then it would make sense to call the drug nonaddictive.
[Thanks to CK for the tip.]