obsessive

adj

1. Prone to cause obsession.

   “The idea is too tempting, it's obsessive.”

2. Having one thought or pursuing one activity to the absolute or nearly absolute exclusion of all others.

   “Hardcore fans' obsessive behavior may take over their lives.”

3. Excessive, as results from obsession.

   “A workaholic's obsessive zeal may lead to success or burnout.”

   “Yes, there were instances of grandstanding and obsessive behaviour, but many were concealed at the time to help protect an aggressively peddled narrative of [Oscar] Pistorius the paragon, the emblem, the trailblazer.”

noun

1. A person who is obsessed, who has an obsession.