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Know when you'll have to take a drug test. Know which drugs are most commonly tested for. Know which drugs employers may also choose to screen for. Know which drugs aren't usually screened for. Understand how a hair test works. Understand how your hair is processed. Immediately stop any drug use. If you're desperate, try a home remedy.

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Drug testing laws vary by state and country. Job applicants are commonly drug tested as part of the hiring process, especially for low or entry-level jobs. In the United States, federal agencies that require drug testing adhere to testing procedures set by the Substance Abuse and Mental Health Services Administration (SAMHSA). Private employers generally have more freedom in their drug testing procedure. However, laws vary from state to state.  In the United States, companies that hire commercial drivers are required to have a drug testing program in place.  Certain employers might require you to be drug tested even after you are hired. Random drug-testing may be part of the terms of employment, or you may be required to undergo a test if you are involved in a workplace accident. Make sure you understand a company's drug testing policy before accepting a job offer. Research your local laws if you are unsure whether certain activities or jobs require drug testing. In the United States, employers that follow SAMHSA testing guidelines generally test for five specific classes of drugs. These drugs are:  Amphetamines (methamphetamine, amphetamines, ecstasy(MDMA)) Cocaine (Powder and "crack" forms) THC (marijuana, hash, edible cannabis products) Opiates (heroin, opium, codeine, morphine) Phencyclidine (PCP, angel dust) Alcohol is occasionally tested for in addition to the above drugs. Private employers are not required to perform the basic SAMHSA test. Many opt for an expanded test that screens for additional drugs. The most common additions are:  Barbiturates (phenobarbital, butalbital, secobarbital, downers) Benzodiazepines (Valium, Librium, Xanax) Methaqualone (Quaaludes) Methadone (a drug used to treat heroin addiction) Propoxyphene (Darvon compounds) Nicotine (and nicotine by-product, cotinine) The following drugs are detectable in a hair test, but are only rarely tested for.   Hallucinogens (LSD, mushrooms, mescaline, peyote) Inhalants Anabolic Steroids Hydrocodone (Oxycodone, Vicodin) After you consume any drug, the active chemicals in the drug will circulate through your body. These chemicals, or certain other chemicals produced when your body processes the drug (called  metabolites), can accumulate in your hair follicles. As a strand of hair grows, its follicle will deposit these chemicals in it. Hair tests look for these chemicals in a small sample of your hair. Hair tests cut a small sample of your hair (usually 1-3 clumps of about 50 strands each). Most cuts are taken from the back of the head so as not to ruin your haircut.  The standard detection window for the hair test is  90 days.  Because hair grows about 1.5 inches (3.8 cm) in 90 days, hairs with a length of about 1.5 inches (3.8 cm) are targeted for cutting. Longer hairs will give a longer window of detection.For instance, a 6-inch long strand of hair can potentially reveal drug use from a year ago. However, 90 days is the most common testing window, so, generally, long strands of hair are cut to 1.5 inches (3.8 cm) before being tested. Depending on the drug and the specifics of the testing process, a hair test may or may not be able to detect whether or not use has been discontinued. For instance, opiates bind tightly to the shaft of hair, while cocaine can migrate along the hair shaft. In this case, certain tests can detect the approximate date of the opiate use based upon its position in the hair shaft, while this is impossible for cocaine.  If no hair is available on your head (you're bald or have a shaved head), hair from other parts of your body can be tested.    Note: Because it can take up to a week for drug-affected hair to grow above the scalp,  hair tests can miss very recent drug use.  For this reason, some employers will also require a urine test, which can detect most drug use within the last few days. Know which tests you will have to take. As soon as you know you'll have to undergo a drug test, stop taking drugs. If possible, cease all drug use before you even begin looking for jobs. Hair tests can detect the use of some drugs, like cannabis, up to 90 days after it's occurred. Because of this, it may be best to stop drug use up to three months before you think you'll be in the job market. If you've used drugs often within the last 90 days and you have a hair test at the end of the week, you may consider using a commercially-available product or a DIY home-method to improve your chances of passing your test.  These methods have not been proven to work in a scientific setting.  They are supported only by individual, unverified stories of success.