Addictive means causing or tending to cause addiction. The present-participle adjective addicting is technically synonymous with addictive, but there’s no reason to use addicting when addictive is a perfectly functional and even versatile word. The trend is to use addicting in reference to nonaddictive things that engender repeated indulgence (e.g., a great television show or a video game), but there’s no reason addictive can’t fill this role.
The use of addicting in place of addictive is a common peeve among people who care about these things, but it isn’t an error, and no doubt there are many readers who have no problem with it.
For example, addictive could replace addicting in these sentences:
Running road races can get addicting, so for those who love it there are three 5Ks this month … [Providence Journal]
The show was, in a word, addicting. [San Francisco Chronicle]
Not surprisingly, helicopters can be addicting, so much so that some tour customers become students. [Seattle Post Intelligencer]
And these writers show that there is nothing wrong with using addictive in reference to things that are not drugs, alcohol, or other addictive substances:
Angry Birds is famous for its cute characters, charming visuals and immensely addictive gameplay. [Wired]
This is of course part of the addictive nature of Apple products. [Wall Street Journal]
As I drifted from turn to turn I felt weightless and wonderful – the addictive sensation of powder skiing at its best … [Telegraph]