When shooting up, the majority of IDUs will, after inserting the needle into a vein, "backdraw" blood into the syringe to make sure that they really have hit the vein. The reason is that if drugs are injected into human tissue outside the bloodstream, they will be absorbed by the liver, dampening the high.
大多數的靜脈注射毒癮者施打毒品時，通常在將針頭插入血管後，會先「倒抽」把血液抽出來，以確認針頭已進入血管。