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Drugs & Health Blog

How Do Drugs Get Into a Person’s Hair?

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The NIDA Blog Team

You’ve probably heard of different kinds of drug tests. But did you know that a person’s hair can be tested for drugs? Drugs can get into hair from inside the body, or from outside.

Reaching the hair

For a drug to get into the hair from inside, it first has to enter a person’s bloodstream. This happens when a drug is injected into a vein, or when it’s smoked, snorted, or swallowed.

Once in the bloodstream, the drug travels to every part of the body, including the hair. Some drugs, such as morphine, cocaine, nicotine, and amphetamines, then attach to the melanin (which gives hair its color) in each strand of hair.

As far as drugs entering the hair from the outside, when drugs are smoked, some of the smoke or vapor enters the air. Some drugs, such as nicotine and heroin, then can easily enter a person’s hair and attach to melanin. Even with a good shampoo, some of the drug will stay inside the hair.

Testing hair for drugs

No matter how a drug reaches the hair, researchers have developed very sensitive chemical techniques to detect drugs there. If it got to the hair from inside the body, tests can even tell when the drug was used. A drug found in the hair root was used very recently; if it’s closer to the end of the hair, the drug may have been used months before.

There’s a catch, though: If a person’s hair tests positive for a drug, how do the testers know if the drug came from the person’s environment (from secondhand smoke, for instance) or from drug use? As testing techniques get more precise, it will become easier to answer that question. And, that’s why urine and blood are also often tested for drugs.

Learn when and why teens may get tested for drug use.

Drug Tests
Comments posted to the Drugs & Health Blog are from the general public and may contain inaccurate information. They do not represent the views of NIDA or any other federal government entity.


I'm wondering how long the drugs stay in the hair, or if they stay indefinitely.

Great question! We still aren’t sure how long drugs stay in a person’s hair. It depends on many factors. If you’d like to learn more about drug testing, please visit

I'm curious about how long it takes an ingested drug to reach the it 1 or 2 days or closer to a week?

Great question! We aren’t sure how long drugs take to reach a person’s hair. Similar to our answer about how long drugs stay in a person’s hair, how long it takes a drug to reach someone’s hair also depends on many factors, including how a person used the drug.

This post was very helpful because it helped me understand how if you really want to see if a person was taking drugs, is to test to see if its in there hair because it will stay in the hair a lot longer than in teh blood stream.
I had no clue that drugs could affect you. This just proves drugs can affect in every way possible. I find it strange that it can affect your hair but it’s a good thing to know.
Does the drug stay in the hair longer than anywhere else? Is it more effective than doing a blood or urine test? Will this replace a drug/urine rest?
When will researchers come up with the answer to tell the difference between first hand and second hand drug use? Is it more effective than doing a blood our urine test? Will this replace a drug/urine test?

These are very thoughtful questions! If you’re interested in learning more about what we do know on the topic of drug testing, this web page has more information:

I got tested positive for cocaine on a hair follicle and I don’t even do cocaine how is that possible

We recommend you consult with a medical or health professional to discuss your questions.

Which health care professionals would you recommend we talk to

We recommend speaking with your primary care doctor, who can refer you to another specialist if needed.

How much crack cocain do u need to smoke for it to be in the hair follicles

Hi Emily. It’s safe to say that even a small amount of cocaine can show up in hair follicles. When a drug is injected into a vein, or when it’s smoked, snorted, or swallowed, it gets into a person’s bloodstream, and from there, gets to their hair follicles.

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