Topical Minoxidil (Rogaine): SULT1A1 and Treatment Response

Topical minoxidil is applied to the scalp as a solution or foam. It is a prodrug: an enzyme must convert it into an active form. In hair follicles, the sulfotransferase enzyme SULT1A1 helps convert minoxidil into minoxidil sulfate, which supports its hair-growth effects. Goren et al., 2014.

1. Topical minoxidilApplied to the scalp
2. SULT1A1Helps activate minoxidil in hair follicles
3. Minoxidil sulfateThe active form

Research measuring sulfotransferase activity in plucked hair follicles has linked lower activity with poorer response to topical minoxidil. This connects the enzyme's function to an outcome people care about: how well treatment works. Read the follicular enzyme study.

rs1042028 changes the SULT1A1 protein itself. At position 213, the amino acid arginine is replaced by histidine. Researchers refer to this change as p.Arg213His or R213H; it is the characteristic change in SULT1A1*2. Older literature commonly uses rs9282861, an identifier since merged into rs1042028. Variant annotation and identifier history.

The variant assessed by Gene2Rx

Gene	SULT1A1
Variant	rs1042028, formerly rs9282861
Protein change	p.Arg213His (R213H), associated with SULT1A1*2
Variant type	Missense: changes one amino acid in the enzyme
Functional finding	Reduced enzyme activity and thermostability in experimental studies

What the experiments show

Human platelet studies. Raftogianis and colleagues measured SULT1A1 activity and thermostability in human platelets and examined alleles in people with contrasting enzyme characteristics. SULT1A1*2 was consistently associated with lower activity and lower thermostability. Raftogianis et al., 1997.

Direct comparison of the two enzyme forms. Li and colleagues expressed the Arg213 and His213 forms in cells. The His213 form had significantly lower activity toward the thyroid hormone T3 and reduced thermostability, while apparent substrate affinities were similar. These experiments directly demonstrate an effect on enzyme function. Li et al., 2001.

Additional biochemical evidence. Nowell and colleagues combined platelet measurements with experiments using recombinant enzymes. The His213 enzyme was less efficient at activating two tested compounds, adding evidence that this amino-acid change can alter catalytic function. Nowell et al., 2000.

Reduced thermostability means the enzyme's activity is less resistant to heat in laboratory testing. Together with the activity measurements, it helps characterize the altered protein. These studies tested enzyme function using other substances; they were not trials measuring hair regrowth with minoxidil.

Decreased function has a specific meaning

The evidence supports describing this as an experimentally characterized decreased-function variant. The enzyme retains activity, and the size of the effect depends on the substance being metabolized and the experimental conditions. For example, one study found similar sulfation rates for the two forms with paracetamol and p-nitrophenol. Wong et al., 2002.

The number of SULT1A1 gene copies can also influence overall activity. rs1042028 therefore identifies one meaningful contributor to enzyme function, rather than measuring a person's entire sulfation capacity. Hebbring et al., 2007.

The rationale for assessing rs1042028 brings together the variant's measured effects on SULT1A1, the enzyme's role in minoxidil activation, and research on treatment response. This gives the Gene2Rx guideline a functional basis.

A 2025 retrospective pharmacogenetic study reported an association between rs1042028 and minoxidil response, including poorer response in people with the C/T genotype. That finding supports the relevance of this variant to treatment outcomes. Because the study included varied treatment regimens, it does not establish a precise chance of success for each genotype with a particular topical product. Gaboardi et al., 2025.

What this means for screening: a known functional variant in an enzyme involved in drug activation is useful genetic context for understanding treatment response. Prospective studies of specific topical regimens will help establish how accurately rs1042028 predicts individual outcomes.

A DNA result does not measure enzyme activity in your hair follicles. It identifies an inherited factor that can contribute to that activity. Hair-loss biology, other genetic factors, the treatment used, and consistent application also matter.

Gene2Rx reports this result using SULT1A1*1 and *2. At the tested rs1042028 site, *1 represents C (Arg213) and *2 represents the decreased-function T variant (His213). Your diplotype shows whether zero, one, or two copies of *2 were identified.

Reading your SULT1A1 result

Result	Interpretation
*1/*1C/C	Normal Function Your SULT1A1 result indicates normal function at the tested site. Other factors also influence your response to topical minoxidil. Recommendation: Use topical minoxidil as directed and assess hair growth over time with your clinician.
*1/*2C/T · One *2 copy	Decreased Function Your SULT1A1 result suggests reduced activation of topical minoxidil, which may contribute to a weaker response. Recommendation: If hair growth is limited despite consistent use, discuss additional or alternative treatments with your clinician.
*2/*2T/T · Two *2 copies	Decreased Function Your SULT1A1 result suggests reduced activation of topical minoxidil, which may contribute to a weaker response. Recommendation: If hair growth is limited despite consistent use, discuss additional or alternative treatments with your clinician.
Indeterminate	Indeterminate Your SULT1A1 result could not be determined confidently from the available DNA data. Recommendation: Base treatment decisions on your clinical assessment and response to topical minoxidil.

These star-allele labels describe the rs1042028 site assessed by Gene2Rx. Other SULT1A1 alleles and gene copy-number changes are not assessed by this targeted test.

The v4 Full Report includes this assessment for both array and WGS (whole-genome sequencing) customers. Array processing can use imputation, which infers a result from nearby genetic markers when the variant is not directly measured. If the upload cannot support a confident result, the assessment remains indeterminate.

Your result gives you and your clinician a specific genetic finding to consider alongside your treatment history. If topical minoxidil has helped less than expected, carrying the decreased-function variant offers a plausible contributing explanation. It cannot establish the cause of a disappointing response on its own.

Useful points to discuss include your hair-loss diagnosis, which product you use, how consistently and how long you have used it, side effects, and changes in hair growth. The Gene2Rx guideline provides response information; genotype alone should not determine starting, stopping, dose changes, or switching formulations.

Does this apply to oral minoxidil?

This interpretation is for topical minoxidil, including scalp solutions and foams. It does not predict response to oral minoxidil. A study of oral treatment found a different relationship between follicular enzyme activity and response, illustrating why results should be interpreted in the context of the formulation. An rs1042028 result alone is not a reason to switch to oral treatment. Jimenez-Cauhe et al., 2024.

What about other hair-loss medicines?

Our finasteride and dutasteride pages explain those medicines, but Gene2Rx does not provide genetic assessments for them. You can explore their roles alongside minoxidil in the hair-loss medication overview.

Functional characterization of SULT1A1

• Raftogianis et al. (1997). Phenol sulfotransferase pharmacogenetics in humans. Human platelet activity, thermostability, and SULT1A1 alleles.
• Li et al. (2001). Characterization of human liver SULT1A1 allozymes. Experimental comparison of Arg213 and His213 enzyme forms.
• Nowell et al. (2000). Relationship of SULT1A1 genotype to sulfotransferase phenotype. Platelet measurements and recombinant enzyme experiments.
• Wong et al. (2002). Association of the SULT1A1 R213H polymorphism with colorectal cancer. Includes enzyme assays illustrating that functional effects depend on the substrate and assay.
• Hebbring et al. (2007). Human SULT1A1 gene: copy number differences and functional implications. The contribution of gene copy number to enzyme activity.

Minoxidil activation and treatment response

• Goren et al. (2014). Novel enzymatic assay predicts minoxidil response in the treatment of androgenetic alopecia. Follicular sulfotransferase activity and topical treatment response.
• Gaboardi et al. (2025). 26-SNP panel study of androgenetic alopecia therapy. Genetic associations with treatment response, including rs1042028.
• Jimenez-Cauhe et al. (2024). Hair follicle sulfotransferase activity and effectiveness of oral minoxidil. Evidence specific to oral treatment.