High levels of prescription or
nonprescription medicines may be caused by a drug overdose, either accidental
or intentional. A drug overdose may be caused by one large dose of medicine or
long-term overuse of a medicine. Interactions between medicines also can cause problems, especially if you start taking a new medicine. A high level may mean that a person is not
taking his or her medicine correctly or that the medicine is not being properly
processed by the body.
Low levels of prescription or
nonprescription medicines may mean that a person is not taking his or her
What Affects the Test
Reasons the results may not be
- Some drugs that may be mistaken for others. For
example, some cough medicines that do not contain
narcotics may be identified as a
- Drinking or eating some types of food (such as a food
containing poppy seeds).
- Having blood in the urine.
- The amount of time between taking the drug and collecting the
- Not having a large enough urine sample.
Many medicines may change the results of this test. Be sure
to tell your doctor about all the nonprescription and prescription medicines
What To Think About
- In general, laboratory methods are better able
to detect drugs in urine than in blood. Compared to urine and blood tests, saliva tests can provide a less invasive and equally accurate way to detect drugs.
- The reliability of toxicology tests
depends on the methods used by the laboratory. Occasionally drugs that have
been taken are not detected (called a
false-negative result) or drugs that have not been
taken are detected (called a
- Results that
mean drug use or abuse should always be confirmed by at least two different
test methods because of the possibility of false results, the possible
consequences (such as arrest or loss of a job), and the legal aspects of drug
- Attempts to block or interfere with test results by drinking
large amounts of water or taking other substances may be dangerous and usually
do not change the test results.
- For suspected drug abuse, a trained
person may need to watch the urine, blood, or saliva collection, and every person who
handles the sample must sign a "chain of custody" document that is kept
together with the test report. This prevents the substitution or loss of the
urine, saliva, or blood sample.
- A breath test may be used to estimate blood
alcohol level. To learn more, see the topic
Self-Test for Breath Alcohol.
- Standard tests can't detect inhalant abuse. Inhalant abuse is when someone inhales or sniffs common household products to "get high." Such products include—but are not limited to—glues, nail polish remover, lighter fluid, spray paints, and cleaning fluids.