Is Pornography Addictive?

Yes.

It is worth acknowledging that pornography addiction is not a specific diagnosis in the DSM-V.  However, there is certainly a pattern of behavior that people consistently call "pornography addiction" that is troubling, distressing and disruptive over a span of time.  I have heard some neurologists comment that pornography use activates the same parts of the brain as other known addictive behaviors and that it prompts the approximate release of dopamine (a feel-good neurochemical) equal to cocaine use.

The reason it is not a diagnosis appears to be that the determining psychologists are often loathe to risk stigmatizing people's sexual behavior and preferences, which is fine.  

Pornography use can also lead to tolerance, needing to look at "harder" material to achieve the same effect, and some element of withdrawal.  Now the withdrawal will not be physical in my experience, but it can take the form of anxiety, depression, irritability.  Over time, pornography can also undermine romantic relationships and contribute to the dissolving of marriages and families.  

The good news is that help is possible.  This problem is way more common than you might think.  Don't be afraid of reaching out for the help you might need.