When she first started using cocaine, helena really enjoyed the positive feelings that she got from the highs. after some time of using, however, she found that the "lows" that she experienced when she came off of the drug were too unpleasant to bear, and thus she was now using just to avoid experiencing those unpleasant feelings. helena's cocaine addiction would best be explained from the

Opponent-process theory

Explanation:

The opponent- process theory is based on the idea that every time you are going to need a higher amount of something in order to get the same sensation since your body is going to have the tendendy to develop kind of a habit.

Let's say for example that you are scared of something like a snake, at the begining, it's going to be so hard to face the fear and dare to touch one, but after doing it the first time the fear is going to reduce little by little and at the end you will touch them feeling no discomfort or disgust.

In Helena's case the opponent-process is working the other way round, since every time in order to get the same cool sensation she will need a higher quantity of the thing that is making her have those nice sensations, in this case, cocaine.