Short answer: No. Finasteride lowers DHT, the hormone the body makes from testosterone, not testosterone itself. The Propecia (finasteride 1 mg) label says DHT falls by 65% within 24 hours of a tablet, while average testosterone and estradiol levels rise by about 15% and stay in the normal range. The label found no meaningful change in LH or FSH, the signals that tell the testes to make testosterone.
Testosterone is turned into a stronger hormone, dihydrotestosterone (DHT), by an enzyme called 5-alpha reductase. The Propecia label (section 12.1) says there are two types of this enzyme. Type II is found mainly in the prostate, seminal vesicles, hair follicles and liver and makes about two-thirds of the DHT in the blood; Type I, mainly in skin and liver, makes the other third. Finasteride is about 100 times more selective for Type II.
MedlinePlus describes it in plain terms: finasteride treats male pattern hair loss by blocking the body's production of a male hormone in the scalp, and treats an enlarged prostate the same way. That hormone is DHT, not testosterone.
| Hormone | What the label reports |
|---|---|
| DHT in the blood | 65% lower within 24 hours of one 1 mg tablet |
| Testosterone | Average rose about 15% from baseline, within the normal range |
| Estradiol | Average rose about 15% from baseline, within the normal range |
| LH, FSH and prolactin | No clinically meaningful changes |
| Cortisol, TSH, thyroxine, blood fats, bone density | No effect |
Testosterone goes up slightly because less of it is being turned into DHT. The label also says finasteride does not bind the androgen receptor and has no androgenic, antiandrogenic or estrogen-like effects of its own. In healthy men, it did not change how LH and FSH responded to GnRH, which the label reads as the brain-to-testes hormone loop being unaffected.
Normal testosterone does not mean no side effects. In three 12-month hair loss trials (section 6.1), decreased libido was reported by 1.8% of men on Propecia vs 1.3% on placebo, erectile dysfunction by 1.3% vs 0.7%, and an ejaculation disorder by 1.2% vs 0.7%. Overall, 3.8% of men on Propecia reported one or more of these vs 2.1% on placebo. The label says these resolved in men who stopped, and in most who kept taking it.
After approval, the label also lists reports of sexual problems that continued after stopping, male infertility or poor semen quality, testicular pain, and depression and suicidal thoughts (section 6.2). Postmarketing reports cannot show how often these happen. More detail is on Propecia side effects.
The Propecia label does not address use alongside testosterone therapy. On TRT, the enzyme finasteride blocks is the same one that turns the testosterone you take into DHT. Whether it suits someone on TRT is a decision for the prescriber; see hair loss on TRT for what the testosterone labels say about hair.
Two other label points matter. Finasteride lowers PSA, the prostate screening test: in men 18 to 41 on Propecia, average PSA fell from 0.7 to 0.5 ng/mL over 12 months (section 5.2), and the label says any confirmed rise from the lowest value should be checked. And a woman who is or may become pregnant should not handle crushed or broken tablets (sections 5.1 and 8.1).
If you start finasteride while on TRT, logging the start date next to your lab results and any changes you notice makes the picture clearer at the next review. Dose Track keeps both on one timeline.
Read more on Dose Track: Propecia side effects · Finasteride vs dutasteride · Minoxidil vs finasteride · Pattern hair loss: finasteride, minoxidil and more · Missed a Propecia dose