Since you're missing the options, im going to explain the exercise so that you can fill the blank with the correct option.
Drug dealers 'cut' drugs to make them cheaper, by adding other substances with the drug. This is very dangerous and can be fatal.
Some substances can cause interaction with the drug, or form hard deposites(because it doesn't dissolve) in the organs, or yet cause overdose because it's harder to know the exact quantity of drug and easier to take to much.