While 1mg and 5mg Finasteride produce similar DHT reduction (70% vs 73%), some patients report better density outcomes at higher doses. The question of whether 5mg is worth the trade-off has persisted since Merck developed both Propecia (1mg, for hair loss) and Proscar (5mg, for benign prostatic hyperplasia). Your tracking data can answer this question for your individual biology in a way that clinical averages cannot.
This article is for informational purposes only and does not constitute medical advice. Consult a healthcare professional before starting or changing any treatment.
Understanding the Two Doses
Finasteride exists at two standard doses for two different FDA-approved indications.
Propecia (1mg): The Hair Loss Dose
Finasteride 1mg was approved by the FDA in 1997 specifically for male pattern hair loss. At this dose, it inhibits type II 5-alpha reductase, the enzyme that converts testosterone to DHT. The result is approximately 70% reduction in serum DHT levels within weeks of starting treatment.
Clinical outcomes at 1mg:
- 80 to 90% of men halt further hair loss progression
- 65% experience measurable regrowth
- Side effects (sexual) reported in 2 to 4% of users
- Half-life of approximately 6 hours (but DHT suppression lasts longer due to enzyme binding)
Proscar (5mg): The Prostate Dose
Finasteride 5mg was approved earlier (1992) for treating benign prostatic hyperplasia in older men. It produces approximately 73% reduction in serum DHT. Many hair loss patients and clinics prescribe 5mg tablets that are then split into quarters (1.25mg) as a cost-saving measure.
The small difference between 70% and 73% DHT suppression at the serum level has led many physicians to conclude that 1mg captures nearly all of finasteride's hair benefit. But the story is more nuanced than serum DHT alone.
Why the Dose Debate Persists
If 1mg and 5mg suppress serum DHT almost identically, why do some patients swear by the higher dose?
Serum DHT vs Tissue-Level DHT
Serum DHT levels are easy to measure with a blood test, but they do not perfectly reflect DHT concentration at the hair follicle. The follicle exists in a microenvironment where local 5-alpha reductase activity, androgen receptor density, and tissue drug concentration all influence the amount of DHT reaching the androgen receptor.
Some researchers have hypothesized that 5mg achieves slightly higher tissue concentrations in the scalp, producing marginally greater local DHT suppression even when serum levels look similar. This hypothesis has not been definitively proven or disproven.
The Dose-Response Curve
Finasteride's dose-response curve for DHT suppression is logarithmic, not linear. Most of the DHT-lowering effect occurs between 0.2mg and 1mg. Going from 1mg to 5mg adds very little additional suppression in blood tests. The curve looks like this:
| Dose | Approximate Serum DHT Reduction |
|---|---|
| 0.2mg | ~60% |
| 0.5mg | ~65% |
| 1mg | ~70% |
| 2.5mg | ~72% |
| 5mg | ~73% |
The diminishing returns are clear. Each dose increment above 1mg adds progressively less DHT suppression while adding proportionally more side effect exposure.
Individual Metabolic Variation
Not every patient metabolizes finasteride identically. Fast metabolizers may clear the drug more quickly, and some researchers suggest these individuals could benefit from higher doses or more frequent dosing. Without pharmacogenomic testing (which is not standard practice), your tracking data is the best proxy for whether your current dose is optimal.
Head-to-Head Tracking: What to Measure
If you are considering a dose change (or trying to decide between 1mg and 5mg as a starting dose), here is how to set up a proper comparison.
Before Changing Dose
- Compile your existing tracking history. You need at least 6 months (ideally 12) of data on your current dose as a baseline.
- Take comprehensive photos. Hairline, temples, midscalp, crown, and overall top-down view. Same lighting, same distance, same time of day.
- Record current side effects. Document your current side effect status honestly. This becomes your pre-change reference.
- Get a serum DHT test (optional but informative). A blood test showing your current DHT level on 1mg provides a concrete number to compare against a future test on 5mg.
After Changing Dose
Follow this tracking protocol for at least 12 months:
Weeks 0 to 8: Possible adjustment shedding. Some patients report a mild shed when changing dose, similar to the initial shed when first starting finasteride. Track shedding but do not interpret it as a negative signal.
Months 3 to 6: Early density assessment. Compare photos against your pre-switch baseline. Look for subtle changes in hair caliber (thickness) as well as count. Diameter changes often precede count changes.
Months 6 to 12: Meaningful comparison window. By month 12 on the new dose, your tracking data should show whether the change produced a measurable improvement over your previous dose.
The Metrics That Matter
When comparing 1mg vs 5mg in your own tracking, focus on:
- Hair count per cm² in target areas: The most objective metric. AI-powered tracking excels here.
- Hair diameter/caliber: Thicker individual hairs contribute more to visual density than additional thin hairs. This is a more sensitive indicator of DHT suppression improvements.
- Miniaturization ratio: If 5mg is providing better tissue-level DHT suppression, you should see a decrease in the ratio of miniaturized to terminal hairs.
- Recession line stability: Is your hairline holding better on the higher dose?
The Side Effect Trade-Off
This is the critical consideration that tracking alone cannot resolve. For cost comparisons between the two, see the finasteride cost guide.
Sexual Side Effects by Dose
| Side Effect | 1mg Incidence | 5mg Incidence |
|---|---|---|
| Decreased libido | 1.8% | 3 to 5% |
| Erectile changes | 1.3% | 3 to 5% |
| Decreased ejaculatory volume | 0.8% | 2 to 3% |
| Gynecomastia | 0.4% | 1 to 2% |
| Any sexual side effect | 2 to 4% | 5 to 8% |
These numbers come from the respective clinical trial data for Propecia (hair loss) and Proscar (BPH). The BPH population is older on average, which complicates direct comparison. Younger men taking 5mg for hair loss may have different rates, but controlled data in this population is limited.
Monitoring Side Effects During Dose Escalation
Keep a simple weekly log during the first 3 months after any dose change:
- Libido (1 to 5 scale, subjective)
- Sexual function (any changes noted)
- Mood (any notable shifts)
- Breast sensitivity (yes/no)
- Other (brain fog, fatigue, or any new symptoms)
If new side effects emerge after increasing to 5mg, the straightforward approach is to return to 1mg. In most cases, side effects resolve within 1 to 4 weeks of reducing the dose.
The Cost Angle: Quarter-Tablet Strategy
One reason 5mg finasteride enters the conversation is cost. Generic Proscar (5mg) is often cheaper per milligram than generic Propecia (1mg). Many patients buy 5mg tablets and split them into quarters, producing ~1.25mg doses at a fraction of the per-pill cost.
This is a legitimate cost-saving strategy widely used in clinical practice. The resulting 1.25mg dose is functionally equivalent to 1mg for DHT suppression purposes. It does not, however, justify taking the full 5mg tablet for hair loss unless you and your doctor have specifically decided on that dose.
When 5mg Might Be Worth Considering
A dose increase from 1mg to 5mg might be reasonable if:
- You have been on 1mg for 12+ months with suboptimal response
- Your tracking data shows stabilization (no further loss) but insufficient regrowth
- You have tolerated 1mg with no sexual side effects
- Your doctor agrees the potential benefit outweighs the increased risk
- You have already optimized other treatment variables (added minoxidil, considered PRP)
If you have not yet tried combining finasteride with minoxidil, that combination is likely to produce a larger density improvement than increasing finasteride dose alone. For a comparison with the stronger DHT blocker dutasteride, see the dutasteride vs finasteride comparison.
When to Stay at 1mg
Stay at 1mg if:
- Your tracking data shows good response (progressive improvement or stable maintenance)
- You experience any side effects at 1mg
- You have not yet given 1mg a full 12-month trial
- The marginal theoretical benefit does not justify the known increase in side effect risk for your situation
Let Your Data Decide
The 1mg vs 5mg question cannot be answered by population averages alone. The 3% difference in serum DHT suppression translates to a barely perceptible difference for most patients. But you are not most patients. Your genetics, enzyme activity, receptor density, and metabolic profile are unique.
Start at 1mg. Track rigorously for 12 months. If the data says you need more, discuss 5mg with your doctor. If the data says 1mg is working, stay there.
Ready to measure your finasteride response objectively? Upload your photos at myhairline.ai/analyze and track density, diameter, and miniaturization changes over time with AI precision.
This article is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional before starting, changing, or stopping any treatment.