3-Methyl-4-OH-Phenylglycol (MHPG) is a byproduct of the central nervous system’s norepinephrine (NE) metabolism. MHPG metabolizes to vanilmandelic acid (VMA) in the liver using the enzymes alcohol dehydrogenase and aldehyde dehydrogenase. Urinary MHPG was originally thought to represent CNS sympathetic output, but is now known to be principally derived from peripheral neuronal NE metabolism.

MHPG has been widely studied as a marker to predict response to medications used in mood disorders or as a biomarker to monitor pharmacotherapies.

3-Methyl-4-OH-phenylglycol is the breakdown product from norepinephrine, but it may also be produced from epinephrine to a lesser extent.

3-Methyl-4-OH-Phenylglycol (MHPG) is a byproduct of the central nervous system’s norepinephrine (NE) metabolism. MHPG metabolizes to vanilmandelic acid (VMA) in the liver using the enzymes alcohol dehydrogenase and aldehyde dehydrogenase. Urinary MHPG was originally thought to represent CNS sympathetic output, but is now known to be principally derived from peripheral neuronal NE metabolism.

MHPG has been widely studied as a marker to predict response to medications used in mood disorders or as a biomarker to monitor pharmacotherapies.

The marker, 3-methylglutaconic acid in high values indicates a reduced ability to metabolize the amino acid, leucine. This abnormality is found in the genetic disease, methylglutaconic aciduria and in mitochondrial disorders.

The marker, 3-methylglutaconic acid in high values indicates a reduced ability to metabolize the amino acid, leucine. This abnormality is found in the genetic disease, methylglutaconic aciduria and in mitochondrial disorders.

The marker, 3-methylglutaconic acid in high values indicates a reduced ability to metabolize the amino acid, leucine. This abnormality is found in the genetic disease, methylglutaconic aciduria and in mitochondrial disorders.

The marker, 3-methylglutaconic acid in high values indicates a reduced ability to metabolize the amino acid, leucine. This abnormality is found in the genetic disease, methylglutaconic aciduria and in mitochondrial disorders.

3-methylglutaric acid is an organic acid classically associated with two distinct leucine pathway enzyme deficiencies.

3-methylglutaric acid is an organic acid classically associated with two distinct leucine pathway enzyme deficiencies.

3-methylglutaric acid is an organic acid classically associated with two distinct leucine pathway enzyme deficiencies.

3-methylglutaric acid is an organic acid classically associated with two distinct leucine pathway enzyme deficiencies.

3-methylglutaric acid is an organic acid classically associated with two distinct leucine pathway enzyme deficiencies.

3-Methylhippurate is a Xylene Metabolite.

Xylene is found in many solvents (paints, perfumes, etc.). Used in insecticide\pesticide application. Metabolized to Methylhippurate, which is measured in urine. 

3-Methylhippuric Acid (3MHA) is a substance your body makes when breaking down m-xylene, a solvent found in everyday products like paints, varnishes, adhesives, cleaning agents, pesticides, and fuels. Testing urine for 3MHA provides a clear measure of recent xylene exposure.

For 3-Methylhippuric Acid (3MHA), a moderate level in urine indicates:

• Above baseline exposure to m-xylene (higher than expected background levels), but not in the high or toxic range.

• Likely reflects recent or regular contact with products containing xylene (paints, varnishes, adhesives, fuels, industrial solvents).

• Suggests the body is actively metabolizing and excreting xylene, meaning your detox pathways are working, but exposure is enough to be measurable and noteworthy.

• Often tied to occupational or environmental exposure, rather than accidental overexposure or acute poisoning.

What Moderate Means Clinically

• Not alarming on its own — it doesn’t necessarily mean severe toxicity.

• Worth paying attention to — ongoing moderate exposure can contribute to cumulative toxic burden, especially affecting the nervous system, mood, sleep, and energy.

• Action point — review likely sources of xylene, reduce exposure where possible, and support detoxification (hydration, nutrition, clean air/ventilation).

Key Takeaway

A moderate 3MHA result is a signal of meaningful xylene exposure, but not a red-flag level. It’s an opportunity to identify where xylene is entering your environment and take steps to minimize contact, preventing progression toward higher, more concerning levels.

Methylhippuric Acids (MHAs) are metabolites of xylene (dimethylbenzenes).

Xylenes are widely used as solvents in products including paints, detergents, pesticides, fuel, perfumes, and exhaust fumes.

The main effect of inhaling xylene vapor is depression of the central nervous system (CNS), with symptoms such as headache, dizziness, nausea, and vomiting.

Long-term exposure may lead to irritability, depression, insomnia, agitation, extreme tiredness, tremors, hearing loss, impaired concentration, and short-term memory loss.

A condition called chronic solvent-induced encephalopathy, commonly known as "organic solvent syndrome" has been associated with xylene exposure.

Both 1-methylhistidine and 3-methylhistidine are histidine metabolites which have been proposed as markers of meat intake. Note that some confusion exists in the literature regarding the numbering of atoms in the imidazole ring of histidine – 1 versus 3 – and thus, there is caution with interpretation and clinical significance of these two markers.

3-methylhistidine is a constituent of actin and myosin, the contractile proteins of skeletal muscles. Urinary excretion of 3-methylhistidine may be a result of muscle breakdown or consumption of meat fibers. Unlike 1-methylhistidine, 3-methylhistidine has been shown to increase in fasting states indicating catabolism of muscle tissue. Therefore, this marker is more variable with regards to animal protein consumption.