Finasteride on TRT: Oral vs Topical, Sexual Side Effects and What the FDA Has Said

The Short Answer

Men on TRT ask about finasteride for one reason: hair. Testosterone therapy raises DHT, and DHT drives male pattern hair loss in men who are prone to it. We cover the broader hair-loss options in our guide to the DHT tax on TRT and TRT and hair loss.

This article goes deep on one drug. It covers what finasteride does to your hormones on TRT, oral vs topical, the sexual side-effect evidence and what the FDA has actually said.

What Finasteride Does to DHT and Testosterone

Finasteride is a selective inhibitor of type II 5-alpha reductase, one of the enzymes that turns testosterone into dihydrotestosterone (DHT). According to the Propecia (finasteride 1 mg) prescribing information:

• A 1 mg dose suppresses serum DHT by about 65% within 24 hours.
• It lowers DHT in both the scalp and the blood.
• In the label's studies, average testosterone rose about 15% from baseline and stayed in the normal range.
• Its half-life is short: about 5 to 6 hours in men 18 to 60 and about 8 hours in men over 70.

The label figures come from men making their own testosterone. On TRT, your testosterone level is set mainly by your dose. Your routine labs will show whether adding finasteride shifts your numbers.

The one trial that tested testosterone plus finasteride

The most direct evidence is a 12-month randomized trial by Borst and colleagues (Am J Physiol Endocrinol Metab, 2014). Sixty men aged 60 and older with low testosterone were randomized to testosterone enanthate 125 mg weekly or placebo, with finasteride 5 mg daily or placebo.

• DHT: testosterone raised DHT; finasteride lowered it.
• Prostate: testosterone alone increased prostate volume by about 11.4 cm³. With finasteride added, prostate volume changed by about −1.7 cm³.
• Benefits: gains in fat-free mass, strength and spine and hip bone density came from testosterone, and finasteride didn't significantly reduce them. The fat-free-mass gain was numerically smaller in the finasteride group, but the difference was not statistically significant, and a small trial can't rule out a modest effect.
• Hematocrit: rose with testosterone; finasteride didn't change that.

Caveats matter here. The trial used 5 mg of finasteride, five times the hair-loss dose, and 125 mg of testosterone weekly, which the authors call higher than replacement. It enrolled older men, only about 40 of the 60 completed it, and its reported outcomes were muscle, bone and prostate, not sexual side effects. The authors note that non-significant results shouldn't be read as proof of no effect. It suggests that blocking DHT doesn't clearly cancel testosterone's main physical benefits. It doesn't tell you how you'll feel on the combination.

Sexual Side Effects: What the Evidence Shows

This is the question most men care about. The data point in one direction: the risk is real, but in trials the extra risk is small in absolute terms.

A 2018 meta-analysis in Acta Dermato-Venereologica pooled 15 randomized, placebo-controlled trials (4,495 men, mostly men with hair loss). It found 5-alpha reductase inhibitors raised the relative risk of sexual side effects about 1.57-fold. For finasteride 1 mg specifically, the relative risk of erectile dysfunction was about 1.99, with a wide margin of error (95% confidence interval 1.10 to 3.60). Doubling a small baseline rate still leaves a small absolute rate, but it isn't zero.

Persistence after stopping

The Propecia label's postmarketing section lists sexual dysfunction that continued after the drug was stopped. That includes erectile, libido, ejaculation and orgasm problems. Postmarketing reports can't establish how often this happens. They're the reason the label mentions it at all.

The TRT complication

None of these trials studied men on TRT. Libido and erections can also shift when a TRT dose changes. If you start finasteride at the same time as a dose change, you won't know which change caused what. Changing one thing at a time makes side effects easier to trace, so ask your prescriber how they want to sequence it.

FDA Label Changes and Safety Communications

Here's what regulators have formally done, as of October 2026:

• 2022, suicidal ideation added to the Propecia label. In a June 8, 2022 response to a citizen petition (Docket FDA-2017-P-5787), the FDA required suicidal ideation and behavior to be added to the label's postmarketing adverse reactions. The FDA said it could not conclude that a causal link was established. It denied requests for a boxed warning and for new Warnings and Precautions on depression, suicidality and persistent erectile dysfunction.
• Current label. The postmarketing section now lists depression, suicidal ideation and behavior, and sexual dysfunction continuing after discontinuation. It also lists male infertility or poor semen quality, testicular pain, and breast tenderness, enlargement and male breast cancer.
• Prostate cancer warning. In a 7-year prostate cancer prevention trial using finasteride 5 mg, high-grade (Gleason 8–10) cancer occurred in 1.8% of finasteride users vs 1.1% on placebo. The label says 5-alpha reductase inhibitors may increase the risk of high-grade prostate cancer.
• April 22, 2025, FDA alert on compounded topical finasteride. Covered in the next section.

Europe went further in 2025. In May 2025 the European Medicines Agency's safety committee (PRAC) confirmed suicidal ideation as a side effect of finasteride 1 mg and 5 mg tablets, frequency unknown. It added a patient card to 1 mg packs. The committee also found benefits still outweigh risks. It found no evidence linking suicidal ideation to finasteride skin sprays. For mood changes, the committee advised patients to seek medical advice and, for those taking 1 mg tablets, to stop treatment.

Oral vs Topical Finasteride

Topical finasteride appeals to men on TRT because it promises local DHT blocking with less whole-body exposure. There's some evidence for that idea, and a regulatory catch.

What one manufacturer-funded topical trial showed

A phase III randomized trial by Piraccini and colleagues (JEADV, 2022) tested a 0.25% finasteride spray in 458 men aged 18 to 40 in Europe for 24 weeks. Hair counts rose about 20.2 hairs with the spray, 21.1 with oral finasteride and 6.7 with placebo. Serum DHT fell about 34.5% with the spray vs 55.6% with oral 1 mg. Peak blood levels of finasteride were more than 100 times lower with the spray. Treatment-related sexual side effects were 2.8% with the spray, 3.3% with placebo and 4.8% with oral finasteride.

That's one specific, manufactured European formulation over 24 weeks. The trial was funded by the spray's manufacturers, its oral-finasteride arm was small (85 men), and it wasn't designed to compare sexual side-effect rates, so the authors' safety conclusions are inferred from the lower DHT and drug levels. It doesn't tell you how a U.S. compounded solution of a different strength and vehicle behaves.

What the FDA said about compounded topicals

On April 22, 2025, the FDA alerted providers, compounders and consumers to risks with compounded topical finasteride, alone or combined with ingredients like minoxidil:

• There are no FDA-approved topical finasteride products. Compounded versions are not FDA-approved, and the FDA hasn't evaluated their safety, effectiveness or quality.
• The FDA received 32 adverse event reports from 2019 to 2024. Reported effects mirrored oral finasteride's: erectile dysfunction, decreased libido, anxiety, depression, suicidal ideation, brain fog, insomnia, fatigue and testicular pain. Skin irritation was also reported.
• Most reports said the effects continued after the product was stopped.
• The agency flagged the risk of transferring the product to others, especially women.

As of October 12, 2026, FDA's Drugs@FDA data still lists finasteride only as oral products.

Prices are from Cost Plus Drugs' price list and HealthRX's hair-loss page, checked October 12, 2026. HealthRX's oral minoxidil 1 mg/finasteride 1.25 mg capsule, $35/mo on a 3-month plan, is also a compounded combination and not FDA-approved.

If you already use testosterone cream or gel, a topical finasteride adds a second product that can rub off on a partner or child. See our guide to cream absorption and transfer.

PSA, Fertility and Your TRT Labs

Adding finasteride changes how some of your TRT monitoring should be read.

PSA reads lower

Finasteride lowers PSA. In Propecia's trials in men 18 to 41, average PSA fell from 0.7 to 0.5 ng/mL at 12 months. In older men with BPH on the 5 mg dose, PSA drops by about 50%. The label says any confirmed rise from your lowest PSA on finasteride should be evaluated, even if it's still within the normal range.

PSA is a core TRT safety lab, so make sure whoever reviews your results knows you take finasteride. Ask whether they want a fresh PSA before you start. More in our PSA and TRT guide.

Fertility

The label's postmarketing reports include male infertility and poor semen quality, with improvement reported after stopping. TRT is a fertility issue on its own: the Endocrine Society guideline recommends against testosterone therapy in men planning fertility in the near term. If fertility matters to you, read TRT and fertility and raise both drugs with your prescriber.

Mood and sexual baseline

Note your libido, erections and mood before you start finasteride. With a baseline, it's much easier to tell your prescriber whether something changed. Our guide to TRT and mental health covers mood tracking on TRT.

The Bottom Line

Finasteride is a reasonable option to discuss if TRT is speeding up hair loss. The one small trial we found suggests it doesn't significantly undo testosterone's physical benefits, and it may limit prostate growth, but that trial can't rule out a modest effect. Expect a small but real risk of sexual side effects. Regulators have formally recognized mood effects, and topical versions sold in the U.S. are compounded and not FDA-approved.

Before you start, ask your prescriber:

1. Should I use oral generic finasteride or a compounded topical, given the FDA's 2025 alert?
2. Do you want a PSA now, before finasteride lowers it?
3. Should we avoid changing my TRT dose at the same time, so we can tell what caused any side effect?
4. What symptoms should make me stop and call you?

No hair-loss treatment works for everyone, so ask your prescriber how long a fair trial should be before you judge it. If you're still choosing a TRT clinic, start with our clinic comparison.