Low testosterone · Telehealth for men · Canada & USA
Testosterone and hair loss: what DHT, genes and TRT really do
Pattern hair loss comes from DHT, a hormone made from testosterone, acting on scalp follicles that your genes make sensitive to it. In a study of 373 men, blood testosterone was not linked with hair loss, and low T thins body hair rather than causing balding. The Endocrine Society lists pattern balding in men with a family tendency as an uncommon side effect of TRT. Finasteride and dutasteride lower DHT; in trials, testosterone still built muscle and bone alongside them, but they can affect libido, semen and PSA. Diffuse or sudden shedding usually has another cause, such as thyroid, low iron, illness, stress or fast weight loss. We help men in Canada and the USA find the cause, plan the right labs and build one plan for their hormones and their hair.
Part of our low testosterone and andropause guide for men in Canada and the USA.
Testosterone and hair loss at a glance
Androgenetic alopecia, or male pattern hair loss, is the most common kind of hair loss in men. MedlinePlus Genetics (US National Library of Medicine) estimates it affects 50 million men in the United States, and more than 50 percent of men over 50 have some degree of hair loss; the European S3 guideline puts it at up to 80 percent of Caucasian men with age. Here is what the research says about the questions men ask most.
| Question | What the research shows | What it means for you |
|---|---|---|
| Does high T cause balding? | 373 men: blood testosterone not linked with hair loss | Follicle sensitivity matters more than your level |
| Does low T cause hair loss? | Low T can thin armpit and pubic hair | Scalp thinning usually has another driver |
| What drives pattern loss? | DHT plus inherited sensitivity: the AR gene and 63 gene regions | Family history is a good guide |
| Does TRT cause hair loss? | Uncommon, weak evidence, mostly with a family tendency | Plan for it if you are already thinning |
| Finasteride, dutasteride | Finasteride 1 mg: 107 to 138 more hairs than placebo over two years | Judge results at six to twelve months |
| With TRT? | Trials: muscle, strength and bone gains kept | Read PSA with the drug in mind |
| Other causes | Shedding after illness or stress, thyroid, low iron, fast weight loss | Simple labs check most of these |
DHT and 5-alpha reductase: how follicles shrink
An enzyme called 5-alpha reductase turns part of your testosterone into dihydrotestosterone (DHT), a stronger androgen. MedlinePlus explains the effect on hair: each strand normally grows for 2 to 6 years, rests for several months, then sheds, and too much androgen stimulation shortens that growth period, so strands come back shorter and thinner, and regrowth is delayed. The FDA label for finasteride notes that balding scalp has miniaturized follicles and more DHT than hairy scalp. In men the loss follows a pattern: the hairline recedes at the temples and the crown thins.
Does low testosterone cause hair loss, or does high T?
Neither, as a rule. In a population study from Greifswald, Germany (Kische and colleagues, JAMA Dermatology, 2017), researchers measured sex hormones in 373 men by mass spectrometry and found no link between total or free testosterone or androstenedione and hair loss or its stage. They concluded that sensitivity to androgens at the follicle, not the amount in your blood, explains pattern hair loss. Low testosterone does affect hair in one way: the Endocrine Society lists loss of armpit and pubic hair as a specific sign of testosterone deficiency. If your scalp is thinning and you also have low drive, fatigue or fewer morning erections, check the full picture with low testosterone symptoms.
Genetics: your mother’s side and many more genes
The strongest single factor is the androgen receptor (AR) gene, the receptor DHT acts on. A German study (Hillmer and colleagues, 2005) called variation in this gene the cardinal prerequisite for early-onset pattern hair loss, and because AR sits on the X chromosome, it comes from your mother’s side. It is not the whole story: a 2017 meta-analysis of 10,846 men with early-onset balding and 11,672 controls (Heilmann-Heimbach and colleagues) found 63 gene regions linked with male pattern baldness, together explaining about 39 percent of the variation. So look at both sides of the family, and at your own hairline over time.
Does TRT cause hair loss?
TRT brings low testosterone back into the normal range, and more testosterone means more raw material for DHT. The Endocrine Society’s 2018 guideline sorts the effects: acne, oily skin and a higher red cell count have a clear link with TRT, while male pattern balding in men with a family tendency is uncommon, with weak evidence. The form can matter: the guideline notes moderately high DHT levels with testosterone gels and underarm solution, of unknown significance. If you are already thinning, plan for it: keep levels in the normal range rather than above it, take baseline photos of your hairline and crown, and decide early whether DHT-lowering treatment fits your goals. Our guide to TRT side effects covers the rest.
Finasteride and dutasteride: the basics
Both drugs block 5-alpha reductase, so less testosterone becomes DHT. Finasteride blocks the type II enzyme; a 1 mg tablet cuts serum DHT by 65 percent within 24 hours, says the FDA label. In two trials of 1,553 men aged 18 to 41 (Kaufman and colleagues, 1998), men on finasteride 1 mg had 107 more hairs than placebo after one year and 138 more after two, counted in a one-inch circle at the crown, while men on placebo kept losing hair. Dutasteride blocks types I and II and lowers DHT further: 94 percent at 0.5 mg versus 73 percent for finasteride 5 mg in a one-year trial. It stays in the body for weeks (half-life about five weeks, versus about four and a half hours for finasteride). In a 2022 network meta-analysis of 23 studies, dutasteride 0.5 mg raised total hair count more than finasteride 1 mg after about six months. The European S3 guideline recommends finasteride 1 mg for men over 18 with mild to moderate pattern loss, judging the response at six months (sometimes twelve), with topical minoxidil as another option, and dutasteride as a second step if finasteride has not worked after a year. To keep the benefit, treatment has to continue.
Canada and the USA: Health Canada authorizes finasteride 1 mg (Propecia, sold since 1998) for male pattern hair loss, and finasteride 5 mg and dutasteride (Avodart, since 2003) for an enlarged prostate only. The FDA approved Propecia in 1997. Dutasteride is approved for hair loss in Japan and South Korea, so in North America it is used off-label.
Finasteride or dutasteride with TRT
Men on TRT often ask whether blocking DHT cancels the benefits. The trials say no. In the 5-alpha Reductase Trial (Bhasin and colleagues, JAMA, 2012), 139 men aged 18 to 50 received graded testosterone doses with or without dutasteride: gains in lean mass, strength and sexual function, and changes in red cells and prostate size, did not differ. In 60 men aged 60 and over with low testosterone (Borst and colleagues, 2014), a year of testosterone raised strength, lean mass and bone density and cut body fat whether or not they also took finasteride 5 mg, and finasteride fully prevented the 11.4 cm³ prostate growth seen with testosterone alone. A 2014 review called the combination safe and effective so far and asked for longer studies. Two practical points: finasteride lowers PSA (in men 18 to 41 on 1 mg, from 0.7 to 0.5 ng/mL over a year; by about half with 5 mg in older men), so PSA needs a baseline and is read as a trend; and any confirmed rise from your lowest value on the drug deserves a look, says the FDA label.
Fertility, libido and mood on DHT blockers
Fertility: at the 1 mg hair-loss dose, a trial of 181 men aged 19 to 41 found no significant change in sperm count, motility or shape over almost a year (Overstreet, 1999). At higher strength, finasteride 5 mg and dutasteride 0.5 mg lowered total sperm count by 34.3 and 28.6 percent at six months in 99 healthy men, changes the authors called mild and likely to recover after stopping (Amory, 2007). TRT lowers sperm production on its own, so if children are in your plans, see TRT and fertility. Libido: in year one of the finasteride 1 mg trials, 3.8 percent of men reported a sexual side effect versus 2.1 percent on placebo; most resolved, and rates fell to 0.3 percent or less by the fifth year. The FDA label also lists sexual problems that continued after stopping; the FDA reviewed 421 reports, 59 lasting at least three months after stopping. Mood: both labels warn of depression and suicidal thoughts. Health Canada’s 2026 review continues to find a link with finasteride and is adding the warning to dutasteride. Tell someone you trust early if your mood shifts.
Other causes of thinning hair in men
The pattern is the first clue: a 2026 review (Walker and colleagues) separates shedding (diffuse), alopecia areata (round patches) and androgenetic alopecia (patterned). Shedding (telogen effluvium) follows a trigger such as illness, surgery, poor nutrition, a new medication or infection, usually shows up three to four months later and grows back gradually once the trigger is gone (Bergfeld, 2026; Malkud, 2015). Thyroid problems and low iron are worth ruling out; in men, low iron also means looking for the source, such as bleeding in the gut (Trost, 2006). Fast weight loss counts too: a 2026 meta-analysis of 17 studies linked GLP-1 drugs such as semaglutide and tirzepatide with more hair loss (odds ratio 1.40), mostly shedding tied to nutrient gaps during weight loss. See weight-loss drugs and testosterone. Stress can trigger shedding and also weighs on testosterone, which is why we look at both.
Labs worth asking for
The 2026 review recommends a thyroid test (TSH), a complete blood count and iron studies for hair loss, and the Endocrine Society confirms low testosterone with repeat early-morning tests. If you are on TRT or considering finasteride or dutasteride, add a PSA baseline before you start and hematocrit and PSA on treatment; free testosterone and SHBG help when total T is borderline. We help you plan the order and timing, and read the results with you. Our supplement plans start from those results, so you top up only what is low; too much iron, for example, can overload the body (Trost, 2006). The full list is in labs to ask for, and SHBG is explained in free vs total testosterone.
How Odin helps with low T and hair loss
Odin Health Labs is an andropause and low-T telehealth service for men in Canada and the USA. On a free call we go through your symptoms, hair and family history, medications, supplements, weight, sleep and stress, plus any labs you already have. We help you work out which pattern you are dealing with, plan the right tests, read the results with you in plain language, and build one written plan that covers your hormones and your hair. If TRT or a DHT blocker is on the table, we help you weigh the trade-offs and track PSA, hematocrit and your hairline over time. Our health coaching keeps the plan going, and functional health looks at the whole picture.
Assessment
A telehealth review of your symptoms, hair pattern, family history and medications, anywhere in Canada or the USA.
Labs
Testosterone, thyroid, iron, PSA and hematocrit at the right time, so you see what changed.
Hair tracking
We help you set baseline photos of your hairline and crown and compare them at each check-in.
A written plan
Hormones, hair and habits in one plan, with clear next steps.
From thinning hair to a plan
Here is how we work with you, start to finish.
- Step 1
Talk it through
On a free call we go through your hair, family history, energy, drive and any treatment so far.
- Step 2
Get a baseline
Morning testosterone, thyroid, iron and PSA, plus hairline photos.
- Step 3
Fix what is fixable
Low iron, thyroid, sleep, stress and weight, with coaching to keep it going.
- Step 4
Recheck and decide
Repeat labs and photos show what moved; we map out your TRT and hair options.
Sources (checked October 17, 2026)
- Bhasin S, Brito JP, Cunningham GR, et al. Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab 2018;103(5):1715–1744. doi.org/10.1210/jc.2018-00229
- Kanti V, Messenger A, Dobos G, et al. Evidence-based (S3) guideline for the treatment of androgenetic alopecia in women and in men, short version. J Eur Acad Dermatol Venereol 2018;32(1):11–22. doi.org/10.1111/jdv.14624
- Health Canada. Summary Safety Review: Finasteride and Dutasteride, Assessing the Potential Risk of Suicidal Ideation (2026). dhpp.hpfb-dgpsa.ca safety review
- US Food and Drug Administration. PROPECIA (finasteride) tablets, US label (2022). accessdata.fda.gov Propecia label
- US Food and Drug Administration. Questions and Answers: Finasteride Label Changes (April 11, 2012; archived copy). fda.gov finasteride Q&A (archived)
- MedlinePlus Genetics, US National Library of Medicine. Androgenetic alopecia. medlineplus.gov androgenetic alopecia
- Kische H, Arnold A, Gross S, et al. Sex Hormones and Hair Loss in Men From the General Population of Northeastern Germany. JAMA Dermatol 2017;153(9):935–937. doi.org/10.1001/jamadermatol.2017.0297
- Hillmer AM, Hanneken S, Ritzmann S, et al. Genetic variation in the human androgen receptor gene is the major determinant of common early-onset androgenetic alopecia. Am J Hum Genet 2005;77(1):140–148. doi.org/10.1086/431425
- Heilmann-Heimbach S, Herold C, Hochfeld LM, et al. Meta-analysis identifies novel risk loci and yields systematic insights into the biology of male-pattern baldness. Nat Commun 2017;8:14694. doi.org/10.1038/ncomms14694
- Kaufman KD, Olsen EA, Whiting D, et al. Finasteride in the treatment of men with androgenetic alopecia. J Am Acad Dermatol 1998;39(4):578–589. doi.org/10.1016/s0190-9622(98)70007-6
- Gupta AK, Talukder M, Williams G. Comparison of oral minoxidil, finasteride, and dutasteride for treating androgenetic alopecia. J Dermatolog Treat 2022;33(7):2946–2962. doi.org/10.1080/09546634.2022.2109567
- Gupta AK, Venkataraman M, Talukder M, Bamimore MA. Relative Efficacy of Minoxidil and the 5-α Reductase Inhibitors in Androgenetic Alopecia Treatment of Male Patients: A Network Meta-analysis. JAMA Dermatol 2022;158(3):266–274. doi.org/10.1001/jamadermatol.2021.5743
- Amory JK, Wang C, Swerdloff RS, et al. The effect of 5α-reductase inhibition with dutasteride and finasteride on semen parameters and serum hormones in healthy men. J Clin Endocrinol Metab 2007;92(5):1659–1665. doi.org/10.1210/jc.2006-2203
- Overstreet JW, Fuh VL, Gould J, et al. Chronic treatment with finasteride daily does not affect spermatogenesis or semen production in young men. J Urol 1999;162(4):1295–1300. pubmed.ncbi.nlm.nih.gov/10492183
- Bhasin S, Travison TG, Storer TW, et al. Effect of testosterone supplementation with and without a dual 5α-reductase inhibitor on fat-free mass in men with suppressed testosterone production: a randomized controlled trial. JAMA 2012;307(9):931–939. doi.org/10.1001/jama.2012.227
- Borst SE, Yarrow JF, Conover CF, et al. Musculoskeletal and prostate effects of combined testosterone and finasteride administration in older hypogonadal men: a randomized, controlled trial. Am J Physiol Endocrinol Metab 2014;306(4):E433–E442. doi.org/10.1152/ajpendo.00592.2013
- Nickel JC, Carson CC. Testosterone Supplementation in Hypogonadal Men on 5-ARI Therapy. Sex Med Rev 2014;2(2):75–78. doi.org/10.1002/smrj.27
- Bergfeld WF, Mendez D. Shedding: An updated guide to a common cause of hair loss. Cleve Clin J Med 2026;93(10):616–622. doi.org/10.3949/ccjm.93a.26008
- Malkud S. Telogen Effluvium: A Review. J Clin Diagn Res 2015;9(9):WE01–WE03. doi.org/10.7860/JCDR/2015/15219.6492
- Walker CW, Champigny D, Hartman T, et al. Hair loss: a systematic approach to evaluation and management. JAAPA 2026;39(9):27–34. doi.org/10.1097/01.JAA.0000000000000405
- Trost LB, Bergfeld WF, Calogeras E. Iron deficiency, its treatment and its potential relationship to hair loss (review). J Am Acad Dermatol 2006;54(5):824–844. doi.org/10.1016/j.jaad.2005.11.1104
- Viquez Burboa GU, Flores Guillén MÁR, Duardo González VS. GLP-1 Receptor Agonists and Alopecia: A Systematic Review and Meta-Analysis of Incidence, Risk, Subtypes, and Mechanisms. Skin Appendage Disord 2026. doi.org/10.1159/000553070
Frequently asked questions
Does testosterone cause hair loss?
Not on its own. Pattern hair loss is driven by DHT, a stronger hormone your body makes from testosterone, acting on scalp follicles that are genetically sensitive to it. In a study of 373 men in Germany, blood testosterone and other sex hormones were not linked with hair loss, and the authors pointed to follicle sensitivity instead. Variation in the androgen receptor gene, which sits on the X chromosome you inherit from your mother, is the strongest single genetic factor.
Does low testosterone cause hair loss?
Low testosterone can thin body hair: the Endocrine Society lists loss of armpit and pubic hair as a specific sign of testosterone deficiency. Thinning at the temples and crown is a different process that follows your genes and DHT sensitivity. If your scalp hair is shedding all over, thyroid problems, low iron, a recent illness, stress or fast weight loss are more common causes, and simple labs can check most of them.
Will TRT make me go bald?
Most men on TRT do not lose hair because of it. The Endocrine Society lists male pattern balding in men with a family tendency as an uncommon side effect, with weak evidence. If you are already thinning, TRT can add to what your genes are doing, so it helps to plan for it: keep your levels in the normal range, know that gels give moderately high DHT levels, and track your hairline with photos. We go through all of this with you before and during treatment.
Can I take finasteride while on TRT?
Trials suggest the two can be combined. When DHT was blocked with dutasteride in 139 men, or with finasteride in 60 older men with low testosterone, testosterone still built muscle, strength and bone, and in the older men finasteride prevented testosterone-driven prostate growth. A 2014 review called the combination safe and effective so far but asked for longer studies. Finasteride lowers PSA, so your PSA baseline and its trend need to be read with that in mind.
Does finasteride affect fertility or libido?
At the 1 mg hair-loss dose, a study of 181 young men found no significant change in sperm counts over almost a year. The higher 5 mg finasteride dose and dutasteride lowered total sperm counts by 29 to 34 percent at six months in healthy men, changes the authors called mild and likely to recover after stopping. In the main 1 mg trials, sexual side effects were reported by 3.8 percent of men on finasteride and 2.1 percent on placebo; the FDA label also lists sexual side effects that continued after stopping in some men, and both the FDA and Health Canada list mood changes, including suicidal thoughts. TRT itself lowers sperm production, so if children are in your plans, talk this through early.
How does Odin Health Labs work with my doctor?
Odin Health Labs is an andropause and low testosterone telehealth service for men in Canada and the USA. We work alongside your own doctor: we go through your symptoms, hair history, family history, medications and lab results with you, help you decide which tests to ask your doctor for (such as morning testosterone, thyroid, iron studies and PSA), and build your plan for hormones, sleep, weight and nutrition. Finasteride, dutasteride and TRT are prescription medicines, so we help you prepare clear questions for the doctor who prescribes them, and we can share your plan and results with your doctor if you choose. See our low testosterone overview and our Privacy Policy.
Want one plan for your testosterone and your hair?
A free call is the first step: we go through your symptoms, hair and family history and any labs, then set up a plan with check-ins.