'I was using', 'I have used', 'I have been using', 'I had used' - what is the difference amongst these?

First, is my question right? Does amongst fit here?

Please differentiate the above phrases.

I have used cocaine.

I took cocaine at least once sometime in the past.

I was using cocaine.

In the past, I was a habitual user of cocaine. EDIT: As the comment says, this can also mean a process in the past, e.g. "I was using cocaine when the accident happened" can mean "I was not looking at the road since I was snorting cocaine."

I have been using cocaine.

Starting some time in the past, and including today, I use cocaine.

I had used cocaine.

With my reference point at a time in the past, by that point, cocaine was already taken by me. Better example:

By the time I met my girlfriend, I had used cocaine.

So when meeting the girlfriend, you took cocaine by then already.

BONUS: You missed one:

I had been using cocaine.

Meaning, with a reference point in the past, starting a time before then up to the reference point, I was habitually using cocaine up to and including that point.

Why not put in some other wonky tenses?

I will have used cocaine.

I will have been using cocaine.

Here is a link conjugating it in all its tenseful glory.