A danger with so-called 'casual drug abuse' is that it carries a risk that - over time - it can escalate into habitual drug abuse. This can be the foundation for drug dependency.

How can this happen?

If an individual abuses drugs to feel better or as a way of coping with problems, then there's a good chance that he or she will never learn the life skills necessary for feeling good naturally, or coping with difficult situations. Instead, he or she may always choose to avoid uncomfortable feelings or situations simply by getting drunk or stoned etc.

Here's a make-believe example:

A schoolboy fails an examination. He feels bad and smokes some cannabis to avoid his feelings of shame and disappointment. He begins to do this regularly when he feels down.
He gets older. He loses his job. He's very angry about that, but the old level of drug abuse no longer numbs his emotions. So he gets some tranquillisers from his doctor - and soon starts to abuse them. They become his new emotional painkiller.
He gets older still. A member of his immediate family dies. He's grieving. The old ways of killing his pain are not enough. He needs more. He begins to get drunk every day.

We can substitute alcohol or other drugs anywhere in here - it's all the same.

He has never learned any other way of dealing with uncomfortable feelings