Both finasteride and dutasteride are 5-alpha reductase inhibitors — oral medications that work by reducing dihydrotestosterone (DHT), the hormone responsible for follicle miniaturisation in androgenetic alopecia. But they’re not the same drug, and the differences matter when choosing between them.
This guide breaks down how each medication works, compares evidence at a high level, discusses side effect profiles, and explains how to track either prescribed routine with enough context to review over time. It is separate from spironolactone, another anti-androgen prescription option most often discussed for women with female pattern hair loss.
The Common Enemy: DHT
To understand finasteride and dutasteride, you need to understand DHT.
Dihydrotestosterone (DHT) is a potent androgen derived from testosterone via the enzyme 5-alpha reductase. In men with the genetic predisposition to male pattern baldness, DHT binds to androgen receptors in scalp hair follicles, causing them to shrink progressively over successive growth cycles — a process called follicle miniaturisation.
There are two types of 5-alpha reductase:
- Type I — predominates in skin, sebaceous glands, and liver
- Type II — predominates in hair follicles, prostate, and genital skin
This distinction is critical for understanding why finasteride and dutasteride produce different results.
How Finasteride Works
Finasteride (Propecia, generic) selectively inhibits 5-alpha reductase type II. At the 1 mg dose used for hair loss, it reduces scalp DHT by approximately 60–70% and serum (blood) DHT by approximately 70%.
Because finasteride targets type II — which is highly expressed in hair follicles — it’s an efficient, targeted approach.
Standard dose: 1 mg/day oral FDA-approved: Yes, for male pattern baldness
How Dutasteride Works
Dutasteride (Avodart) is a dual inhibitor, blocking both type I and type II 5-alpha reductase. This broader blockade reduces serum DHT by approximately 90% — significantly more than finasteride.
This greater DHT suppression translates to measurably better outcomes in head-to-head studies, at the cost of a broader hormonal effect.
Standard dose: 0.5 mg/day or 0.5 mg/week (off-label) FDA-approved: For benign prostatic hyperplasia, not hair loss (prescribed off-label for hair loss)
Efficacy Comparison
Multiple studies have compared finasteride and dutasteride for hair loss:
| Study | Duration | Dutasteride Result | Finasteride Result |
|---|---|---|---|
| Harcha et al. (2014) | 24 weeks | +12.2 hairs/cm² | +7.3 hairs/cm² |
| Boyapati et al. (2022) | 12 months | Superior regrowth | — |
| Phase III trials | 12 months | Hair count: +109.7/cm² | Hair count: +75.6/cm² |
The consensus across available evidence is that dutasteride produces more hair regrowth than finasteride, particularly at the vertex, due to its deeper DHT suppression.
However, finasteride has decades of safety data and remains the first-line pharmacological treatment recommended by most dermatologists.
Side Effect Comparison
Both medications share a class of side effects related to sexual function — reduced libido, erectile dysfunction, reduced ejaculate volume — because DHT plays a role in sexual function.
| Side Effect | Finasteride | Dutasteride |
|---|---|---|
| Sexual dysfunction | ~2–4% | ~4–6% |
| Breast tenderness | Rare | Rare |
| Depression | Small increased risk | Similar |
| Post-discontinuation persistence | PFS reported (rare) | Reported, less studied |
| Onset of sexual SE | Weeks to months | Weeks to months |
For most men, side effects are mild or absent. It’s worth noting that clinical trial rates of sexual dysfunction in placebo arms are often similar to active treatment arms, suggesting significant nocebo effect.
Important: Discuss your medical history, including any cardiovascular conditions or prostate issues, with a prescribing physician before starting either medication. Do not self-prescribe.
Half-Life Difference
The pharmacokinetic difference between these drugs is dramatic and affects how quickly effects wear off if you stop:
| Finasteride | Dutasteride | |
|---|---|---|
| Half-life | ~6 hours | ~5 weeks |
| DHT recovery after stopping | Days to weeks | Months |
Dutasteride’s long half-life means it takes significantly longer to clear your system. This is relevant if you experience unwanted side effects and want to stop quickly.
Which Should You Choose?
This is a decision for you and your prescribing physician. Some considerations:
Finasteride may be preferred if:
- You’re new to 5-ARI treatment and want to start with the standard option
- You want to assess tolerability before escalating
- Your hair loss is early to mid-stage (Norwood I–IV)
- You’re concerned about side effects and want the shorter half-life for flexibility
Dutasteride may be preferred if:
- Finasteride hasn’t adequately slowed your hair loss after 12 months
- You’re experiencing rapid progression and want maximum DHT suppression
- Your dermatologist recommends it based on your pattern and stage
Tracking Your 5-ARI Plan with Track Hair
Regardless of which medication you and your clinician choose, tracking is essential. These routines are usually reviewed across long windows, and without before-and-after photos, adherence history, and notes, it is difficult to assess what happened with any discipline.
Here’s how to track your 5-ARI regimen with Track Hair:
- Add your medication as a daily treatment with a once-daily reminder
- Note your starting dose and medication in the treatment details
- Capture baseline photos before or on day 1
- Record changes in dose, timing, missed days, side effects, or other treatments added to the plan, including minoxidil, spironolactone, procedures, or supportive routines if relevant
- Use planned photo check-ins so reviews happen at meaningful intervals
- Prepare for clinician conversations with a clearer timeline of what you took, what changed, and what the photos showed
Start planning your hair loss treatment routine. Download Track Hair and set up your medication schedule, baseline photos, notes, and review checkpoints today.
| *Related reading: How to Track Minoxidil Progress | Spironolactone Guide | Understanding the Norwood Scale | Finasteride Guide* |