No writer can experience everything. Most of us haven't died, and yet we write about death all the time. Likewise, when we write about grief, we may draw on our own personal experiences, but oftentimes, we let our imagination take control.
Perhaps you can boil down the specific emotions you want to describe into more general emotions: you may not have ever been angry enough to kill anyone, but there may have been times when your anger caused you to behave in an irrational fashion. Likewise, you may never have had an addiction to drugs, but you have probably felt the desperation of needing something so badly that you obsess about it, that can feel your brain twitching from thought to thought, always back to thing it needs. The physiological details can be added through careful study (although in the instance of drugs, avoid just watching Trainspotting or Requiem for a Dream: these films have spawned dozens, if not hundreds, of copycat representations of addiction and they're pretty easy to spot). Do real research into the scenario you want to portray: the more you read, the better.
"Show, don't tell" is a good rule of thumb regardless of how much research or imaginative exploration you do. Readers are very good at filling in the blanks and can empathize with a situation described plainly as much as one portrayed in lush, agonizing detail. This is where your artistry comes into play.