These are various tests to evaluate the type (and roughly measure the amount) of legal and illegal drugs a person has taken.

Toxicology screening is most often performed on blood or urine (the specimens of choice) but can be performed on gastric contents (vomit or lavage fluids) if performed soon after the substance is ingested. Nails or hair can be tested for arsenic and mercury.

Blood is drawn from a vein on the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to fill with blood.

A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

Urine sampling can be a random sample (you are asked to urinate into a container). In some circumstances, you may need to obtain the urine sample in the presence of the nurse or technician (to verify that the urine sample came from you and was not tampered with -- see special considerations).

There is no special preparation; this test is often performed as an emergency test. Inform the health care provider of any prescription and over-the-counter medications you have taken, including the amount and time of ingestion.

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

If a urine sample is used, it involves only normal urination and there is no discomfort.