What Does 500 pg/mg Mean in a Hair Drug Test?
500 pg/mg is a concentration, not a dose. What it means for cocaine and morphine, why the substance changes the answer, and what it cannot tell you.
Published
500 pg/mg means the laboratory measured 500 picograms of a substance in every milligram of hair tested. It is a concentration — how much was found in a set weight of hair — and it is the most precise thing a hair test produces.
What it is not is a dose. The number does not convert into how much of a drug was taken, how many times, or exactly when. And on its own it does not tell you whether the result is high or low, because that answer changes with the substance.
The short version
- pg/mg = picograms per milligram — a measure of how much of a substance is in the hair, not how much was consumed.
- It can’t be converted into a dose or a frequency — there’s no reliable way to turn this number into “X uses” or “Y milligrams taken”.
- The meaning depends on the drug — 500 pg/mg of cocaine is not the same as 500 pg/mg of morphine. Each substance has its own context and ranges.
- Metabolites matter — labs often detect the drug plus the breakdown products your body creates. The full pattern says more than a single number.
- Hair treatments affect results — bleaching, dyeing or straightening can lower the concentrations measured.
- Interpretation is expert work — a forensic toxicologist weighs the number against hair type, passive exposure, prescriptions and medical history before it means anything.
What pg/mg measures
A picogram is one trillionth of a gram. A milligram is one thousandth of a gram. So pg/mg asks a simple question: in a set weight of hair, what weight of the substance is present?
Hair takes up drug molecules from the bloodstream as the shaft forms in the follicle, so a length of hair holds a record of what was circulating while it grew. Head hair grows at roughly 1 cm per month, and laboratories commonly analyse the 3 cm closest to the scalp — about the last three months. The concentration reported is what was measured across that length.
That is a measurement of deposition. It is not a measurement of consumption, and the two are separated by everything the body does in between.
Where 500 pg/mg sits, substance by substance
This is the part that surprises most people reading a report for the first time. Against the published low, medium and high bands used for interpretation, the same figure lands in a completely different place depending on which substance it belongs to.
| Substance | Published bands | Where 500 pg/mg sits |
|---|---|---|
| THC | Medium 1 – 10 · High > 10 pg/mg | Far above the high band |
| Fentanyl | Medium 10 – 100 · High > 100 pg/mg | Well above the high band |
| Cannabidiol (CBD) | Low < 50 · Medium 50 – 1,000 pg/mg | Mid medium band |
| Cocaine | Low < 500 · Medium 500 – 5,000 pg/mg | The bottom of the medium band |
| MDMA | Low < 200 · Medium 500 – 7,500 pg/mg | The bottom of the medium band |
| Morphine | Low < 200 · Medium 200 – 3,000 pg/mg | Inside the medium band |
Amphetamine and methylamphetamine are read on a different scale again. The full levels chart carries every substance, along with the eight documented reasons a low, medium or high label can be wrong.
There is no universal rule that makes 500 a lot. Three things turn it into a finding: which substance it belongs to, what was found alongside it, and the laboratory’s own reporting criteria.
Cocaine at 500 pg/mg
500 pg/mg sits exactly at the boundary between the low and medium bands for cocaine.
| Band | Concentration | Published meaning |
|---|---|---|
| Low | < 500 pg/mg | Infrequent recreational use, or incidental contamination where no metabolites are present |
| Medium | 500 – 5,000 pg/mg | Repeat or multiple use occasions |
| High | > 5,000 pg/mg | Regular use |
Sitting on a boundary is precisely the situation where the rest of the report decides the reading. Cocaine testing looks for the parent compound and the metabolites the body produces from it, and the presence or absence of those metabolites is what separates ingestion from contact — which is why use and exposure are read differently. A cocaine figure with no metabolites behind it supports a different conclusion from the same figure with them.
Morphine at 500 pg/mg
500 pg/mg falls inside the medium band for morphine.
| Band | Concentration | Published meaning |
|---|---|---|
| Low | < 200 pg/mg | Occasional exposure, and may appear alongside codeine or 6-MAM |
| Medium | 200 – 3,000 pg/mg | Repeat or multiple use occasions |
| High | > 3,000 pg/mg | Regular use |
Morphine reaches hair from prescribed morphine-containing medicines as well as from other sources, so what accompanies it matters. Codeine commonly appears alongside morphine and points towards codeine-containing medication. 6-MAM (6-monoacetylmorphine) is the marker specific to heroin. A morphine concentration read without checking for either is a number missing its context.
Why metabolites decide the reading
A metabolite is a substance the body produces as it breaks a drug down. Detecting one is evidence the substance passed through the body rather than settling on the outside of the hair.
That distinction is what a concentration alone cannot supply. Several drugs can reach hair externally — handling a substance, or sitting in a room where it is being smoked — and a parent compound will register from that contact. A metabolite will not, because it only exists once the body has processed the drug. The pattern of parent compound and metabolites is therefore the part of the report doing the heaviest work, and it is read together with the number rather than after it.
What a hair test can establish
A hair test can show:
- whether a substance was detected across a historical window — roughly 1 cm of head hair per month
- the concentration of that substance, in pg/mg
- which metabolites were present alongside it
- with segmental analysis, how those findings changed month by month
A hair test cannot establish:
- the dose taken
- the number of occasions a substance was used
- precise timing — it is a monthly record at best, never a daily one
- whether use was intentional, prescribed or accidental
That last point is the reason a concentration is a starting position rather than a conclusion. It is also why a fortnight of heavy use can lift a whole three-month result: a single-length sample is reported as one averaged figure, and the average does not announce which weeks produced it.
What an interpretation weighs
This is where a number stops being useful on its own and expert interpretation begins. An independent forensic toxicologist reviewing a report weighs several things at once that the laboratory certificate does not address.
Why the substance is present. Hair analysis cannot separate intentional use from a prescribed medicine or an accidental ingestion. Passive exposure — second-hand smoke, or handling a substance — can produce a detectable concentration without anyone consuming anything.
How the hair itself behaves. Darker, more porous hair incorporates more of a substance, which lifts a concentration for reasons unrelated to how much was used. Growth rate and metabolism differ between people. Cosmetic processing — colouring, bleaching or straightening — moves the figure in the other direction.
What sits outside the certificate. Prescriptions, medical records and a documented history can each change what a concentration supports.
Whether further testing would settle it. Segmental analysis, or a second sample type, often resolves a picture that a single averaged figure leaves open.
Weighing all of that against one number is what an accurate interpretation requires, and it is the work of a qualified forensic toxicologist rather than something to be read off a chart.
The bottom line
500 pg/mg is a concentration measured in hair. It is a precise, defensible measurement of what was deposited — and it is not a measure of how much was consumed.
How that concentration is read depends on the substance detected, the metabolites found with it, which hair segment was tested, the laboratory’s cut-offs and reporting criteria, the overall pattern across the panel, the characteristics of the hair, and any chemical treatment it has had.
The concentration ranges on this page are provided as general educational information only. They should not be used to interpret an individual result, or to work out how much or how often a drug was used.
Have your result interpreted
Dr Michael Robertson, independent forensic toxicologist, reviews drug, alcohol and steroid results — hair, blood, urine, saliva or breath — whoever carried out the testing, and gives an independent opinion on what a concentration does and does not support.
Request a consultation or a written report. Requests are handled through the clinic.
Frequently asked questions
Can 500 pg/mg be converted into a dose or a number of uses?
No. Hair testing measures how much of a substance was deposited into the hair shaft, and deposition is affected by hair growth rate, pigmentation, porosity, metabolism and cosmetic treatment. There is no published conversion from a hair concentration to milligrams consumed or to a count of occasions, and any figure presented as one is unsupported.
Does bleaching or colouring change the number?
Yes. Bleaching, permanent colouring and chemical straightening can reduce the concentrations measured in hair, sometimes substantially. How much any individual sample is affected depends on the strength of the treatment, how often it was applied and over what period, so it is not predictable from the result alone. Declare any chemical treatment when the sample is collected so the interpretation can account for it.
My report shows 500 pg/mg but no metabolites. What does that mean?
It is a finding worth having interpreted rather than read off a chart. For several substances the parent compound alone can reach hair from the outside — handling a substance, or being in a room where it is smoked — while the metabolite is only produced once the body has processed it. The published low band for cocaine explicitly covers incidental contamination where no metabolites are present. What that means for a particular report depends on the substance, the concentration and the rest of the findings.
Would segmenting the hair change the 500 pg/mg figure?
It can change how the figure is read. A standard 3 cm sample is reported as one number averaged across roughly three months, so a short period of heavier use raises the whole result. Splitting the sample into 1 cm segments reports each month separately, which can show 500 pg/mg as one heavier month rather than a steady quarter. It needs enough hair to divide and it must be requested — a single-length report cannot be segmented after the fact.
