Finasteride is among the most effective drugs for androgenic alopecia. And while side effects are often overstated, it can lead to reduced libido or lowered sperm counts in some men. For this reason, many choose topical versus oral finasteride, hoping to limit the drug’s DHT-reducing effects to the scalp. But at certain doses, even topical finasteride can become systemic. So, to minimize side effects, which finasteride dosage, formula and application is best?
In this article, we’ll review
- About oral versus topical finasteride
- Why topical finasteride can still go systemic
- Why choosing the lowest percentage solution isn’t the only answer
- How to maximize finasteride gains, while minimizing side effects
Finasteride, also known under the brand name Propecia or Proscar, is a prescription medication approved by the FDA for the treatment of androgenic alopecia (AGA). The anti-androgen works by reducing the production of Dihydrotestosterone (DHT), a hormone linked to pattern hair loss. In use since 1992, Finasteride is among the most powerful and well-studied drugs for hair loss.
Oral finasteride stops AGA progression in 80-90% of men and, on average, leads to a 10% increase in hair count over two years.https://www.sciencedirect.com/science/article/pii/S0022202X15529357 For men wanting a “hands-off” approach to hair maintenance, oral finasteride can be an excellent option. With a once-daily pill, it’s expected that hair loss will stop at approximately 6 months, and thereafter, improve.
However, oral finasteride isn’t for everyone. While the risk of side effects are often overstated online, the drug appears to reduce libido in a certain percentage of men. Oral finasteride can also temporarily lower sperm counts, which might make conception more difficult during its first six months of use. In some men, the use of finasteride appears to increase anxiety and/or depression. While the true incidence and magnitude of these reports are hard to discern, it’s understandable that many are weary of taking this once daily pill.
Fortunately, recent improvements in finasteride’s delivery may mean we no longer need to throw the proverbial baby out with the bathwater.
The biggest reason people seek out topical finasteride (instead of oral finasteride) is because they want to minimize systemic exposure to the drug, and in doing so, localize finasteride’s effects to the scalp.
While research is still in the early stages, evidence suggests that topical finasteride can produce similar levels of hair regrowth compared to oral finasteride, with a significantly reduced incidence of side effects.
Topical finasteride works identically to its oral counterpart: by inhibiting the type II 5-alpha reductase enzyme to reduce DHT. It is designed to target scalp DHT instead of systemic DHT levels.
However, limiting finasteride’s reach to scalp, not serum, DHT is harder than perhaps anticipated. To understand why, let’s take a closer look at scalp versus serum DHT.
Serum vs Scalp DHT
There’s a lot of evidence that the hormone DHT is directly implicated in androgenic alopecia. In fact, research directly links DHT to all three of AGA’s defining characteristics:
- Increased telogen:anagen ratio. DHT’s influence on DKK-1 expression increases hair shedding
- Increased anagen cycling. DHT’s effects on signaling pathways limit the growth phase of hairs
- Hair follicle miniaturization. DHT’s effects on dermal papilla sizing thins hair with each cycle
There are a wide variety of DHT reducers available, including prescription drugs, over-the-counter products, intradermal injections, and even herbal supplements. Finasteride reduces DHT in two ways.
- Oral finasteride reduces DHT everywhere in the body. Beyond just the scalp, it reduces DHT in the blood, brain, and prostate.
- Topical finasteride attempts to reduce DHT only where it is applied – in the scalp – with minimal effects on DHT levels elsewhere.
However, it’s far easier than most realize for topical finasteride to go systemic. And when it does, it potentially reduces DHT everywhere – leading to the very side effects it’s meant to prevent.
Topical Finasteride Can Still Go Systemic
Why? When it comes to lowering DHT (the goal of the drug), finasteride has a highly-sensitive, dose-dependent response curve. This means that while 0.01 mg of finasteride barely reduces any DHT at all, 0.1 mg reduces almost as much DHT as 5 mg, a much larger dose.
This implies that when applying topical finasteride, only a tiny fraction of it needs to go systemic in order to produce the same DHT-lowering effects as oral finasteride. If this happens, the purpose of using the topical formulation is completely defeated.
Research suggests a 1% topical finasteride formulation, applied twice daily, is ‘non-inferior,’ meaning equivalent, to 1 mg oral finasteride tablets.https://www.ncbi.nlm.nih.gov/pubmed/19172031 And while that’s a positive in terms of hair growth, using this amount topically twice daily pretty much guarantees systemic absorption. In other words, if 1% topical is the equivalent of 1 mg oral, we can expect it to reduce serum DHT levels by 71%.
So what if we choose a formula with even lower percentages of the active drug? A study on 0.25% topical finasteride showed just a 35% reduction in serum DHT levels versus 55% for the oral medication, and yet similar outcomes for hair regrowth in both oral and topical groups.https://onlinelibrary.wiley.com/doi/10.1111/jdv.17738
So what if we go even lower? A study on 0.005% alcohol-based topical finasteride instructed participants to use the formulation twice daily, with 1 mL applied per session.https://dx.doi.org/10.3109%2F09546639709160517 This led to no appreciable changes in serum DHT levels… meaning that for this ultra-low topical formulation, there was little-to-no systemic absorption (and presumably, few-to-no side effects). The good news? This group still experienced great hair growth outcomes.
So Just Reach for the Lowest Percentage, Yes?
It’s tempting from the above to infer we’ve reached the end of our story. As long as we reach for the lowest percentage of topical finasteride, we can be free from worries about the drug’s systemic effects. But, reality is a bit more complicated than that.
Systemic absorption isn’t just about dilution percentages. Topical finasteride’s systemic absorption actually depends on (at least) for variables:
- The drug’s formulation. Common carrier agents include alcohol and propylene glycol.
- The amount applied per use. The amount of topical finasteride applied to the scalp greatly varies.
- The application frequency. Applying the drug twice per day can more than double its effects on serum DHT.
- The days of application. Topical finasteride can take many days to “leak” into the blood before its final effects on serum DHT are realized.
For an example, see this figure from a 2014 study measuring how one versus two applications of 1 mL of 0.25% topical finasteride affected serum DHT levels.https://www.ncbi.nlm.nih.gov/pubmed/25074865
Over a 24-hour period, what were the findings?
- One application (i.e., 1 mL of 0.25% topical finasteride) lowered blood DHT levels by ~20%
- Two applications (i.e., 2 mL total) lowered blood DHT levels by ~70%
As such, we need to factor in these variables if we plan on sticking with topical finasteride for the long-term. Otherwise, we risk lowering our DHT levels to the same degree as 1 mg of oral finasteride, which would defeat the purpose of using the topical in the first place.
Topical Finasteride and Serum DHT: What Do The Clinical Studies Say?
Let’s take a closer look at some of the studies mentioned above. In addition to the percentage of active drug in the formula, there are a few more variables to understand. How much of the topical was applied, and which carrier agents were used?
The table below shows how even a .25% formula, for example, can reduce DHT in the serum by 24-70%
Based on this table, our total mg of daily finasteride exposure is probably the biggest factor in determining systemic leakage. And our total daily exposure (in mg) is a function of topical finasteride dilution (%) and the amount (mL) applied daily.
Knowing this, we can turn this table into a chart and sort it by mg of daily exposure. In doing so, we see a clear trend:
The good news? At both extremes of this chart – 0.091 mg and 2.275 mg daily – topical finasteride was shown to produce clinical results in improving hair parameters. Based on this, if we’re going for topical finasteride, we probably want to be prescribed topical finasteride solutions that net us daily exposure volumes of 0.228 mg and lower. After all, at 0.091 mg of topical finasteride daily, no systemic effects on DHT were observed.https://www.tandfonline.com/doi/abs/10.3109/09546639709160517
In other words, low dilutions (i.e., 1-2 mL of 0.005% to 0.02% of topical finasteride) confer significant benefits but at reduced risks of side effects due to lower systemic absorption – provided that guidelines for daily amounts (in mL) are also followed.
So What’s the Perfect Amount and Formula?
Our analyses from member-submitted lab tests and the clinical data suggest that 10-15% of topical finasteride will enter the bloodstream, at least when it’s formulated with alcohol and/or propylene glycol as carrier ingredients (as most compounding pharmacies do). So, if we apply 1-2 mL of 0.005% to 0.02% topical finasteride, this might equate to just 0.01-0.03 mg of systemic drug exposure.
For the overwhelming majority of people, that’s not enough systemic leakage to significantly lower DHT levels in the body. But it is enough to produce great hair loss outcomes.
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Long-story short: stick to 1-2 mL of 0.005% to 0.02% topical finasteride solutions. This equates to roughly 0.1-0.2mg of daily finasteride exposure to the scalp. Any more than that, and there’s risk of significant systemic leakage, which defeats the purpose of using topical finasteride altogether.
How to Maximize Gains and Minimize Side Effects
Maximizing gains while minimizing the side effects of finasteride can be done, but it’s not a perfect science. We’ve outlined several tips below that we think might help. Due to individual variance, the most important step is to always start with testing.
1. Get Lab Tests for DHT
The goal with topical finasteride is to reduce the risk of side effects. To do this, we must minimize the amount of finasteride that leaks into the bloodstream. The best way to do this isn’t to rely on estimated metrics from clinical studies, but to collect personal data.
Get a serum DHT test before using the topical to establish a baseline. Then, DHT levels should be retested at one month to gauge just how much is going systemic. Testing is easier than most expect, and in our experience, the expenses are worth the peace of mind.
If future lab tests deviate from baseline, it’s an indication of just how much topical finasteride is going systemic. According to the clinical data, 30 days of application is more than enough time for finasteride to saturate at its maximum levels in the scalp and serum.
As such, measuring DHT levels after one month of finasteride use offers a great reference point to see if topical finasteride is impacting serum DHT levels. If needed, changes can be made to the application or use frequency depending on any changes to your blood levels of DHT.
2. Understand That DHT Levels Fluctuate Diurnally
Keep in mind, some fluctuation in DHT levels is normal. DHT levels fluctuate throughout the day and across seasons. As such, 15-20% differences across tests are normal and expected. Anything beyond 20% suggests that topical finasteride might be having slight systemic effects.
Because of this fluctuation, however, it’s important to get blood draws done at the same time of day – preferably in the morning and while in a fasted state. Also, try not to make drastic changes to diet, lifestyle, or environment prior to testing. Heavy drinking, deviations from a typical daily diet, the introduction of creatine powders, and/or sleep deprivation can all influence DHT levels and muddy test results. In the 3-5 days prior to the second test, try to keep things as they were when you first went in for testing.
3. Avoid supplementing with Quercetin and/or Creatine
Maintaining systemic DHT levels, while maximizing the effects of finasteride, isn’t just about the drug. There are other activities that could potentially affect DHT levels. Supplementing with quercetin and/or creatine is one common mistake that could impact results.
Studies on mice suggest that quercetin can inhibit the DHT-reducing effects of finasteride.https://joe.bioscientifica.com/view/journals/joe/181/3/493.xmlWhile the translatability to humans has not yet been studied, the dosages used in these mouse models were comparable to what humans typically consume from quercetin supplements. As such, it may be best for those using finasteride to avoid this supplement.
When it comes to creatine, one study found that in training athletes, creatine supplementation increased serum DHT levels by over 70%.https://pubmed.ncbi.nlm.nih.gov/19741313/ While the study was small, we have to reconcile these findings with the reality that for the overwhelming majority of training athletes, creatine is unnecessary. Bodybuilders can still look great without using it, and so can the every-day gym goer. Competitive bodybuilders are, however, a different story.
4. Set Realistic Expectations and Track Progress
Finasteride is the best-studied intervention for androgenic alopecia. In order to appreciate its full effects, consider the following:
- Know the timeline for results. Clinical studies show that finasteride improves pattern hair loss outcomes in 80-90% of men. Having said that, cosmetic degrees of hair regrowth don’t often occur until after 10-12 months of treatment. Moreover, the drug’s full effects typically take two years to manifest, with the biggest degrees of cosmetic regrowth occurring between year one and year two. As such, don’t expect any miracles in the first six months, it may take the full two years to see an effect.
- Track progress. It’s hard to know if something is improving without objective measurements. While not all of us have access to trichoscopic hair-counting equipment, most of us do have a smartphone, which can easily be used to take photos to track progress (particularly when the photosets are standardized). This can be done relatively effortlessly.
Following the tips above allows for the best possible shot at measurable hair growth results, while minimizing the potential effects of systemic DHT reduction.
Oral finasteride works great for male pattern hair loss, but by significantly reducing serum DHT, it can cause unwanted side effects.
Topical finasteride was developed as a solution, with a goal to reduce DHT in the scalp only. But when applied in high percentages or large amounts, it too, can go systemic and reduce serum DHT levels.
To minimize the side effects of finasteride without missing out on the benefits, stick to 1-2 mL of 0.005% to 0.02% topical finasteride solutions. This equates to roughly 0.1-0.2mg of daily finasteride exposure to the scalp.
The best way to ensure a reduced risk for side effects is to track serum DHT levels. Establish a baseline by taking one test before using finasteride, then test again one month later.
Rob English is a researcher, medical editor, and the founder of perfecthairhealth.com. He acts as a peer reviewer for scholarly journals and has published five peer-reviewed papers on androgenic alopecia. He writes regularly about the science behind hair loss (and hair growth). Feel free to browse his long-form articles and publications throughout this site.