Before we dive into the details of dutasteride and its effect on hair growth, there is a very important point that you need to understand, and that is the hormone behind androgenetic alopecia. So, I’ll explain that first, and then we can go into the details of dutasteride.

What Hormone is Responsible for Androgenetic Alopecia?

A century ago, the medical community mistakenly thought testosterone was the cause of balding due to androgenetic alopecia. Men who were castrated to become eunuchs never went bald until they received injections of testosterone.

However, in 1974, Dr. Julianne Imperato-McGinley discovered there was a small group of people in the Dominican Republic that have a genetic defect of Alpha-5 Reductase Type 2. This is the enzyme that breaks down testosterone into dihydrotestosterone (DHT) in the human body.

This discovery was instrumental in differentiating the influences of testosterone versus dihydrotestosterone on the human body.

In the male fetus, testosterone develops the internal genitalia, while DHT develops the external genitalia. Therefore, the male offspring with this genetic defect were born with ambiguous genitalia. 

In the male adult, Testosterone is responsible for: 

1. muscle mass, 
2. bone density, 
3. beard hair thickening, 
4. sexual function (libido, spermatogenesis, sperm morphology/motility). 

In the male adult, DHT is responsible for:

1) patterned hair miniaturization (balding) seen in androgenetic alopecia,

2) hair thickening of the follicle in the nose, ears, & back, 

3) prostate enlargement, 

4) prostate cancer. 

DHT has not been shown to have any beneficial effects in the male adult.

Therefore, these adult men with the genetic defect Alpha-5 Reductase Type 2 live healthy normal adult male lives (i.e., good muscle mass, good bone density, ability to have children) except:

1) they never experience male pattern baldness (MPB)

2) they never develop thick hair in their nose, ears, or backs

3) their prostates never enlarge

4) they never develop prostate cancer.

When the pharmaceutical companies became aware of the beneficial effects of the lack of Alpha-5 Reductase in adult men, they got dollar signs in their eyes, and there was a race to develop competitive inhibitors to Alpha-5 Reductase Type 2.

What Is Dutasteride?

Dutasteride is an Alpha-5 Reductase Type 2 and Type 1 Inhibitor that received FDA-approval. The pharmaceutical company, Glaxo Wellcome (GSK), received FDA-approval for Dutasteride at a dose of 0.5mg (brand name Avodart) for the indication of benign prostate hyperplasia (BPH) in November of 2001. It subsequently received FDA-approval for reducing the risk of Acute Urinary Retention in October of 2002. In 2002, GSK halted its Phase III clinical trials in its pursuit to get dutasteride FDA-approved for androgenetic alopecia. Even though the initial studies showed significant efficacy in treating androgenetic alopecia, GSK stated they stopped the FDA approval studies for commercial reasons and to focus its use on prostate health. Dutasteride has been approved to treat androgenic alopecia in South Korea (2009), Japan (2015), and Taiwan. Doctors in most other countries prescribe it “off-label” for androgenetic alopecia.

Also Read: Minoxidil for Hair Loss: A Guide by Dr. Paul J. McAndrews

How Does Dutasteride Work?

Dutasteride is not an anti-androgen; it is an androgen modulator. It works by competitively inhibiting Alpha-5 Reductase Type 2 and Type 1 enzymes, which inhibit the conversion of a patient’s testosterone into DHT. Therefore, a patient’s testosterone level increases and their scalp DHT levels decrease by 90% when taking Dutasteride, which is significantly greater than Finasteride.

Also Read: Finasteride for Hair Loss: A Guide by Dr. Paul J. McAndrews

How to Take Dutasteride Correctly?

Men experiencing androgenetic alopecia should take a 0.5 mg tablet orally once daily. Try to be consistent (i.e., put it by your toothbrush at night and take it after brushing your teeth). If you forget to take it for a few days, it is not the end of the world, just re-start taking it once a day. 

What Is the Most Effective Dose of Dutasteride? Is More, Better?

Before any drug gets FDA approval, the pharmaceutical company is required to do “dose ranging studies” to determine the most effective dose. In the treatment of BPH, the most effective dose of dutasteride was 0.5 mg. In countries where it’s been approved for the treatment of androgenic alopecia, the dose is also 0.5 mg.

Also Read: Norwood Hair Loss Scale: Stages & Treatment Options

How Often Do I Take Dutasteride? Is It Ok to Take It Less Often?

Before any drug gets FDA approved, they have to perform “dose interval studies”. It was determined that once-a-day dosing is the proper interval for BPH. The serum half-life of Dutasteride is approximately 5 weeks, which is much longer than the serum half-life of Finasteride, which is 4 to 6 hours. This would also mean that if a patient developed a side effect from Dutasteride, this side effect would also last much longer than from Finasteride.

An argument could be made that Dutasteride does not need to be taken daily but can be taken at a longer interval; Unfortunately, this has not been studied. With this knowledge, several Dermatologists prescribe it two to three times per week on an off-label basis for androgenetic alopecia.

Can Dutasteride Be Applied Topically to the Scalp?

The answer is YES. A patient would need to get a doctor to have a pharmacist compound the dutasteride into a solution to be applied topically. This is off-label use of Dutasteride since it is only FDA-approved orally. However, Minoxidil solutions were compounded by physicians “off-label” for years before it finally got FDA-approved topically as Rogaine.

The topical use of Dutasteride has not been studied to determine its efficacy in treating androgenetic alopecia. I do think topical Dutasteride is effective, but I don’t think it’s anywhere close to as effective as oral Dutasteride. 

This is why Oral is better than Topical:

1. Absorption through the stratum corneum of the skin can be a problem
2. It’s not applied to all of the follicles experiencing androgenetic alopecia,
3. Topical application does not inhibit the conversion of the majority of the DHT produced in your body

If Topical Dutasteride is absorbed adequately, it will still only inhibit the local conversion of testosterone into DHT. Whereas the vast majority of a patient’s circulating DHT is converted in the liver, and this circulating DHT will go up to the hair follicles and cause miniaturizing effects in the balding area.

The other potential risk (not seen in Oral Dutasteride use) is that the Topical Dutasteride can get on your pillow. There’s the medical-legal risk of causation for any birth defect in a developing fetus by being absorbed through a pregnant wife’s skin who came in contact with the Topical Dutasteride.

How Long Does Dutasteride Take to Work?

I tell my patients that Dutasteride, in treating androgenetic alopecia, is similar to toothpaste in treating tooth decay. You don’t judge results on a stopwatch, but on a calendar year. Furthermore, what is most important is not what you see but what you don’t see. If you don’t continue to see progressive balding, that’s a great thing. 

Dutasteride, similar to Finasteride, increases hair counts within the first few months, but this does not translate into a visibly significant cosmetic benefit for at least a year, since the hair is growing at a rate of only 1 cm/month, and it’s slowly getting thicker. I tell my patients not to judge results for at least a year.

Does Dutasteride Eventually Stop Working?

Most of my patients see peak improvement in the vertex at 3 years of treatment. After 3 years of Dutasteride treatment, every patient eventually starts thinning. This does not mean it is not working; patients are thinning but at a significantly slower rate than the patients not taking Dutasteride. This is like fluorinated toothpaste, which does not stop tooth decay completely; it just significantly reduces the rate of progression as the patient ages.

Is Dutasteride More Effective in Certain Areas?

Dutasteride, like Finasteride, is more effective in the vertex than the Frontal & Mid Forelock.

Patients taking Dutasteride or Finasteride need to readjust their expectations for results in the frontal and mid forelock. The goal should be “keep your existing hair”, not bringing back the frontal hairline or increasing density. If the goal is to bring back the frontal hairline or increase density to the frontal forelock, that is where hair transplants come in. Dutasteride is still of the utmost importance to keep your existing genetically prone hair in the frontal and mid forelock.

What Happens If You Stop Dutasteride?

If you stop taking Dutasteride, you will lose its benefits within 2 years of discontinuance.

When Is the Best Time to Start Taking Dutasteride?

If hair loss bothers you, and you are starting to see the initial signs of androgenetic alopecia, the simple answer is “the sooner the better”. Dutasteride treats an aging process (androgenetic alopecia), similar to toothpaste treating an aging process (tooth decay). You don’t wait until you only have half your teeth in your mouth before deciding to start brushing your teeth.

Side Effects and Safety

Most of the drug-related side effects are mild to moderate and typically occur during the first six months of treatment.

The statistically significant side effect profile of dutasteride, similar to finasteride, includes sexual side effects. These side effects resolved with the discontinuation of dutasteride

There have been reports that Dutasteride can lower sperm count and spermatogenesis in 20% of users. Therefore, for guys trying to conceive, it’s worth pausing the drug for a few months before.

There are no other statistically significant side effects

Effect on the Prostate

Dutasteride was FDA-approved to treat benign prostate hypertrophy over 20+ years ago. It has beneficial effects by shrinking the size of the prostate and helping with urine flow. Dutasteride lowers the PSA levels in men, but this does not adversely affect the value of the test.

There was a large study that found a statistically significant small increase in the incidence of high-grade aggressive prostate cancer. 

Can Dutasteride Cause a Shedding Phase?

Yes, but it is absolutely nothing to worry about. Starting any medication or having any trauma can cause a patient’s follicles to synchronize and go into a shedding phase, similar to the normal shedding of a cat or a dog. This synchronized shedding is called Telogen Effluvium. It lasts about 2-3 months. There is no treatment, and it self-corrects. Cats and dogs shed like crazy, but they do not go bald because all their follicles continue to produce more hair after the shed hair leaves the follicle.

Dutasteride for Women

Dutasteride is not FDA-approved in women. It is contraindicated in pregnant women. 

Dutasteride is used off-label by many Dermatologists in 3 groups of women:

1. Premenopausal women experiencing androgenic alopecia who are done having children
2. Postmenopausal women who are on Hormone Replacement Therapy that includes testosterone
3. Women who have a scarring hair loss disorder: Lichen Planopilaris

Also Read: Ludwig Female Hair Loss Scale: Stages & Treatment Options

Dutasteride vs Other Hair Loss Treatments

I consider Dutasteride or Finasteride as our best preventative hair loss treatments for men with androgenetic alopecia. I do not believe there’s any benefit to taking both at the same time since they work on the exact mechanisms of action.

Minoxidil, topically or orally, is also effective. Since it works on a different mechanism of action than Dutasteride and Finasteride, I think it is synergistic to be used in conjunction.

I’m not a big believer in PRP right now. The studies showing efficacy with PRP did not have the greatest study designs or endpoints in determining its efficacy. The current PRP study designs and endpoints would never get FDA-approved. I think there’s one absolute truth of PRP: it makes money for doctors.

Also Read: Taiwan’s New Hair Regrowth Serum: Fact or Fiction

The preventative medical treatments and hair transplants for androgenic alopecia are accomplishing two different goals, similar to toothpaste and a dentist in treating tooth decay. Toothpaste slows tooth decay, and a dentist fills a cavity. Similarly, preventative medical treatments slow androgenetic alopecia, where a hair transplant surgeon fills in the cavity caused by the progressive thinning nature of androgenic alopecia.

A patient’s hair restoration goal is what dictates the course of treatment. If the goal is to slow the progressive nature of androgenic alopecia, the preventative medical treatments are the primary treatment. If the goal is to increase the density in a significantly balding area, the medical therapies are not going to accomplish the goal, and hair transplants are necessary to fill in the balding area. However, if the patient is not on the preventative medical therapies, the hair transplant surgeon runs the risk of eventually running out of the limited good genetic hair.

Who Is a Good Candidate for Dutasteride?

Androgenetic alopecia and tooth decay are both progressive diseases of aging and don’t stop until the day a patient dies. Obviously, the ideal time to start preventative medical therapies is early in the course of androgenic alopecia, just like the best time to start brushing your teeth is early. You don’t wait until you have half your teeth left before you finally start brushing your teeth. However, even men who are significantly balding from androgenetic alopecia are still candidates for the preventative medical therapies, just as patients with half their teeth left still should be brushing their teeth.

I typically reserve Dutasteride for patients who have used Finasteride and were not happy with the results after they understand the risks.

My Experience with Dutasteride

Dutasteride is not FDA-approved for androgenetic alopecia. Finasteride blocks only Type 2 Alpha 5 Reductase enzyme, while Dutasteride blocks both Type 1 and Type 2 Alpha- 5 Reductase enzymes. Dutasteride more effectively decreases serum and scalp DHT levels. I do believe Dutasteride is just as effective as Finasteride in treating androgenetic alopecia, and it may be more effective (we just don’t have the studies), but it also carries more risk.

The medical world does not understand the full implications of blocking the Type 1 Alpha-5 Reductase enzyme. However, we do know the implications of blocking the type 2 Alpha-5 Reductase enzyme since there’s a genetic defect in humans that lack the Type 2 enzyme. This unknown of Dutasteride carries more risk than Finasteride. If a patient were to get sexual side effects from Dutasteride, the side effects would last longer after discontinuing Dutasteride than Finasteride. There is also the added risk that Dutasteride may decrease sperm counts and spermatogenesis. I typically reserve Dutasteride for patients who have used Finasteride without side effects and were not happy with their results.