Drugs aren’t cheap. You can end up spending a fortune, especially if you become dependent on one or more different substances.
When you use drug dealers, you’re not just involved with the person who sold you the drugs, you are dealing with the whole chain of dealers. So if it’s a friend selling you the drugs, they will have bought these from a dealer, who will have purchased them from someone else and so on. So if you can’t pay your friend, they may be hassled by their dealer, escalating the situation to someone who may use blackmail or even violence against you or your friend/dealer putting your life in danger.
If you aren’t able to pay, how will you ensure you get the money to pay your debt? Stealing, lying to your family or a friend to get cash?