While Dutasteride inhibits all three isoforms of 5α-reductase (types I, II, and III), Finasteride only inhibits the type II and III isoforms of the enzyme. Dutasteride inhibits a significantly greater percentage of dihydrotestosterone (DHT) in comparison to Finasteride.
Taking Both Finasteride and Dutasteride to Treat Hair Loss
A few years ago, one of this blog’s frequent commentators mentioned taking Finasteride for six days a week and the much stronger Dutasteride for one day a week. This would theoretically limit the side effects from taking the much more potent Dutasteride for all seven days of the week.
I blew off this idea as pointless, since Dutasteride by itself has such a long 5-week half-life (Finasteride has a 6-hr or so half-life). So one might as well just take Dutasteride once or twice a week and completely ignore taking Finasteride to keep things simple. In fact I myself have been taking 0.5mg Dutasteride every two days rather than daily for a couple of years now.
However, a short time after the above commentator made the suggestion, another blog reader made the following comment:
Dan DECEMBER 8, 2016 AT 2:58 PM
I have just been advised by a hair transplant surgeon, that if you combine 1mg finasteride daily with 0.5mg dutasteride once a week, you can expect regrowth. He learnt this from a recent conference he attended. A hair specialist presented a paper which showed good results from combining finasteride regularly with just one capsule of dutasteride per week on top. I’m yet to try this, but am willing to give it a go and just stop the dutasteride if there is no change or bad side effects.
And then yet again, someone else made the below comment last year:
Tom FEBRUARY 8, 2018 AT 6:20 AM
I had been on Propecia alone for 15 years. Noticed hair started to thin again in 2016. Added Avodart in Jan 2017 and I can honestly say my hair is better and thicker than all the years on just Propecia. I take Propecia every day and one 0.5 Avodart once a week. Never had any sides at all. I did have a shed when I added the Avodart, but stick with it and within about 4 months I could feel and see new hairs. My hairline is better than I can remember. It has taken one full year of this dosage to fully appreciate just how effective it has been. I will continue until things change and then reassess, but hopefully that won’t be for a very long time.
Combination Therapy: Finasteride and Low-Dose Dutasteride
While doing research for this post, I came across a 2013 study from Australia that found combination treatment on one male patient quite effective. Finasteride by itself was not working for him, but adding 0.5 mg Dutasteride once per week drastically improved the hair growth results. Before and after photos can be seen in the study.
Over the years I have read 100s of posts by hair loss sufferers who are uncertain about the most efficient dosage of finasteride (brand name Propecia) or dutasteride (brand name Avodart) to take in order to get the best possible outcome in terms of probable hair maintenance (and possible regrowth) versus risk of side effects. A few people have also e-mailed me with questions about this, but I usually refrain from responding or ask them to consult a doctor.
Each person has a different risk tolerance. For many people, a 90 percent chance of hair maintenance (and maybe some regrowth) combined with a 10 percent chance of significant side effects is preferable to a 80 percent chance of hair maintenance combined with a 5 percent chance of significant side effects. For others, the reverse is true. Similarly, some people might be happy with a 60 percent reduction in dihydrotestosterone (DHT) levels, but others are willing to take a higher dose of a drug in order to get a 70 percent reduction.
The majority of people probably do not even look too deeply at finasteride or dutasteride related studies to try and find all the relevant statistics, and instead just prefer to experiment themselves or go with the doctor recommendation. Others are taking unusual doses (e.g., by cutting 5 mg pills into 4 pieces to get 1.25 mg) that are never covered in studies anyway. Furthermore, many people want to adjust the frequency of their drug intake to an unusual one (e.g., 3 times a week instead of 7 times a week) that is almost never covered in finasteride or dutasteride related studies.
In this post, I will discuss some established dosage details based on published studies and data. Thereafter, I encourage people to comment on what dosage and frequency they have tried in the past, and what seems to have worked best. Scientific dosage related feedback is especially welcomed. I am also curious to hear what people think of taking their finasteride or dutasteride before eating versus after eating; in the daytime versus at night; alongside food such as grapefruit that can impact drug effectiveness; and so on.
Prostate v/s Serum v/s Scalp DHT Levels
Before continuing, one thing to note is that most studies on dihydrotestosterone (DHT) reduction measure serum (aka circulating/blood) DHT levels and scalp (aka follicular) DHT levels when it comes to hair loss related discussions. Prostate DHT level measurements are more common in studies looking at BPH, although many hair related studies also mention them. Both finasteride and dutasteride reduce serum DHT levels by a higher percentage than they do scalp DHT levels for all dosages it seems.
Finasteride (Propecia) Dosage Discussion
Finasteride was originally approved in 1992 to treat benign prostatic hyperplasia (BPH — which means enlarged prostates, a problem typically seen in older men). The finasteride dosage used for treating BPH is 5 mg a day (and the original brand name for this dosage version is Proscar (manufactured by Merck), although generics are now commonly used).
In 1997, the US FDA approved finasteride (at a dosage of 1 mg per day) to treat hair loss. The original brand for this product is the infamous Propecia. However, since Propecia was very expensive for many years when generic versions were not available (due to Merck’s now expired patent), people would buy the 5mg Proscar and cut it into 4 pieces and then take 1.25 mg of the drug every day. This strategy worked out to be a lot cheaper. However, note that there is no guarantee that a pill cutter is accurate enough to ensure 1.25 mg finasteride evenly distributed per quarter pill. Moreover, I have even read that the main ingredient in any pill is not evenly distributed throughout.
So perhaps one quarter of Proscar could theoretically have 1.5 mg instead of 1.25 mg, while another could have 1 mg instead of 1.25 mg. I have no idea if such significant variation in ingredient distribution in a pill is common, but it does seem to have logical merit. When I used to cut generic 5 mg finasteride pills into four pieces a few years ago, I always lost some of the pill to crumbling/powder residue.
In any event, taking 1 mg versus 1.5 mg is not likely to be very different when it comes to finasteride. With dutasteride (see next section), small dosage variations have more of an impact. It should also be noted that some people take Propecia aka finasteride every other day rather than every day.
Finasteride is a type II and type III 5α-reductase enzyme inhibitor, meaning that it prevents the conversion of testosterone to DHT by the type II and III isoenzymes. However, it does not inhibit the type I 5α-reductase enzyme so DHT inhibition is not complete. At a dosage of 1 mg, finasteride results in a decrease in serum DHT levels by about 60-70 percent according to several studies I checked. The number for scalp DHT is a bit unclear, with several sources suggesting a reduction from anywhere between 40-65 percent. Prostate DHT levels decline by around 80-90 percent.
Whole doing research for this post, I uncovered something that I had not realized before. According to this study from 1999, It seems like Finasteride is almost as effective at 0.05 mg per day as it is at 1 mg per day or 5 mg per day when it comes to scalp skin DHT levels. And 0.2 mg per day is almost as effective as 1 mg per day or 5 mg per day when it comes to serum DHT levels.
Results quote from the full version of the above study:
Scalp skin DHT levels declined significantly by 13.0% with placebo and by 14.9%, 61.6%, 56.5%, 64.1%, and 69.4% with 0.01, 0.05, 0.2, 1, and 5 mg doses of finasteride, respectively. Serum DHT levels declined significantly by 49.5%, 68.6%, 71.4%, and 72.2% in the 0.05, 0.2, 1, and 5 mg finasteride treatment groups, respectively.
Another unusual study I found was this old one from 1990. They were testing up to 100 mg (!) per day of Finasteride in patients (for 11 days), which seems crazy.
Dutasteride (Avodart) Dosage Discussion
As I mentioned earlier, the biggest drawback of finasteride is that it does not inhibit the 5α-reductase type I isoenzyme, and therefore does not inhibit more than 70 percent or so (depending on dosage) of circulating DHT levels. However, in 2001, the US FDA approved a new drug called dutasteride (initially only sold under the brand name Avodart, with GSK’s patent on the drug having expired in 2015) to treat BPH. This new drug inhibits all three isoforms of 5α-reductase (i.e., type I, II, and III). As a result, almost all circulating DHT is eliminated (serum DHT levels decline by over 90 percent). This results in superior hair growth results in comparison to finasteride, but greater chances of side effects.
For men with BPH, Dutasteride is typically taken at a dose of 0.5 mg per day. Most hair loss sufferers also take the same dosage. While Dutasteride has been approved to treat hair loss in South Korea and Japan, the same has not yet occurred in the US or the EU as of 2017.
A person by the name of Dr. Richard Clark conducted some very important studies during the years immediately preceding and following the approval of Dutasteride for BPH that compared DHT inhibition from various doses of Dutasteride versus Finasteride 5 mg. Below are several highly useful charts from his studies. Note that in the first chart, the lower the better (i.e., greater DHT inhibition).
Linear versus Nonlinear Elimination
A few months ago, commentator “PinotQ” sent me an interesting e-mail that threw another twist into this confusing story. He also referenced this study from 1999. Key quote from his e-mail:
“FYI — About a month ago, I switched my avodart dosage from .5 mg per day to 1mg Monday, 1mg Wed and 1.5mg on Friday. Dutasteride has a non-linear elimination curve meaning the more you take at once, the longer the half life. At a dose of only 0.1 mg/day, the half-life is only around two or three days while at .5 mg it is 4-5 weeks. For this reason, my doctor suggested that 2 pills taken twice a week may be as effective (or more), than 1 pill per day. I am hoping for a little more powerful response going 3 times per week at 2-2-3 as I had read from Dr. Shapiro online that when switching from finasteride to dutasteride, to see renewed effectiveness, you would probably need to be at the 1mg per day dosage level………but this is just all educated speculation.”
Half-Life of Finasteride v/s Dutasteride and Side Effects
Dutasteride has an extremely long half-life of around 4 weeks. On the other hand, finasteride has a half-life of only 6-8 hours. Unfortunately, dutasteride also has higher side effect rates in comparison to finasteride. Most studies indicate that serious side effects are minimal when it comes to both dutasteride and finasteride (less than 5 percent of people get major problems, and even fewer get irreversible side effects). However, it should be noted that most people who are currently taking the more powerful dutasteride have only been doing so for less than 15 years since the drug was only approved for use in 2001. So we still do not know the really long-term ramifications of taking dutasteride.