[Stronico]

The book Never Enough by Judith Grisel is a good addition this field, and probably this book.

Short version - your body longs to be at equilibrium/homeostasis and drugs (alcohol, stimulants, opiates, etc) upset that equilibrium, so your body attempts to return you to your previous state.

There is no free lunch, and a high will be accompanied by a low. The lows come in numerous and surprising forms.

The book is significantly better than my description.