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Side Effects of Topical Finasteride: Review of Current Medical Literature

Author: Dr. Ben Behnam, MD FAAD 

Board Certified Dermatologist 

Oral finasteride, also known as Propecia, is an oral medication that has been prescribed by physicians for decades for hair loss. It works in the majority of patients by reducing hair loss and stimulating hair growth however there are side effects. One of the most concerning side effects are the sexual side effects, which occur in 1.8% to 3.8% of patients who take it. As a result, many physicians have been switching to topical finasteride as an alternative. In recent years, there have been many studies on the efficacy and side effects of topical Finasteride. In this article, we will review the clinical trials and scientific data to evaluate the side effect profile of topical finasteride. 

In one of the first single-blind, placebo-controlled clinical trials of topical finasteride, Mazarella et al.1 (1997) published a study of 52 subjects ranging from 19 to 28 years of age. The patients were treated with topical finasteride 0.005% vs placebo for 16 months. Here were the results.

  • There was a significant reduction in the rate of hair loss after 6 months of treatment.
  • There were no reports of local or systemic side effects.

In another double blind, randomized clinical trial study of 45 male patients, Hajheydari et al.2 (2009) compared oral finasteride 1mg vs topical finasteride 1% for a total of 6 months.

  • Authors concluded that “the therapeutic effects of both finasteride gel and finasteride tablet were relatively similar to each other.”
  • 1 person had erythema of the scalp after application of the topical finasteride. 

In a prospective pilot study conducted in 15 patients for 9 months by Rafi and Katz3 (2011), patients applied a topical solution called NuH Hair, which is a novel topical combination of finasteride, dutasteride, and minoxidil, with the option to add oral finasteride, minoxidil and/or ketoconazole shampoo for 9 months. 

  • Significant growth was demonstrated after 3 months of use of the topical solution.
  • There were no reports of sexual side effects or irritation or redness reported. 

In a randomized clinical study by Tanglertsampan C.4  (2012), 33 male patients ranging between 27 to 49 years old were enrolled to compare the efficacy and safety of a 24 weeks application of minoxidil 3% lotion versus minoxidil 3% combined with 0.1% finasteride lotion.

  • This study showed that finasteride combined with minoxidil is superior to minoxidil alone by itself.
  • Contact dermatitis and redness was observed in 4 patients (24%) using the finasteride + minoxidil combination. No sexual side effects were observed. 

Caserini et al. conducted two pharmacokinetic studies on topical finasteride. In a randomized clinical study of 23 males, Caserini et al.5 (2014) compared topical finasteride 0.25% twice daily vs oral finasteride 1mg once daily for 7 days. They measured DHT and testosterone levels in the serum (systemic DHT levels).

  • Similar reduction in serum DHT was observed by the use of topical 0.25% finasteride twice daily  (68-75% ) and oral finasteride 1mg (62-72%).
  • No sexual side effects were observed. 

In another randomized clinical trial, Caserini et al.6 (2015) did another study involving 50 male patients studying DHT in both the serum and the scalp. 

  • This pharmacokinetic study confirmed that topical finasteride 0.25% (1ml application twice daily) and oral finasteride 1mg (once daily) both have similar reduction in scalp (47-51%) and serum DHT levels (74-76%). No changes in testosterone were observed.
  • In the portion of the study where patients used 1ml of topical finasteride 0.25% twice daily, there were 2 patients (11%) that had the following side effects. Elevated ALT levels, pollakiuria and testicular pain. 
  • The pharmacokinetic of various dosages of the 0.25% topical finasteride were tested as well. Scalp DHT was reduced by about 37-54% when 0.1ml, 0.2ml, 0.3ml and 0.4ml of topical 0.25% finasteride was used, showing relatively similar results to 1ml twice a day application of topical 0.25% finasteride. Serum DHT was reduced by 24% with the use of 0.1ml, 26% with 0.2ml, 44% with 0.3ml and 48% with use of 0.4ml of 0.25% topical finasteride. This testing suggests that lower dosage of topical finasteride may lead to lower reduction of serum DHT levels and thus lower sexual side effects (assuming that serum DHT is solely responsible for the sexual side effects).  
Scalp DHTSerum DHT
Oral FInasteride 1mg51%76%
1ml (twice daily) of 0.25% Topical finasteride47%74%
1ml (once daily) of 0.25% Topical finasteride71%76%
0.1ml (once daily) of 0.25% Topical finasteride 52%24%
0.2ml (once daily) of 0.25% Topical finasteride47%26%
0.3ml (once daily) of 0.25% Topical finasteride37%44%
0.4ml (once daily) of 0.25% Topical finasteride54%47%

In a retrospective assessment and prospective crossover cohort study of 50 male between 20 to 40 years old by Chandrashekar et al.7 (2017), all 50 patients used minoxidil 5% and oral 1mg finasteride for 2 years.They then stopped and their treatment differed.

  • Results showed that 80% to 84.4% of these patients maintained good hair density while on the topical combination of minoxidil 5% + finasteride 0.1% treatment for 1 year.
  • No sexual side effects were reported. 

The studies8 above demonstrate that topical finasteride has clinically proven, evidence-based, scientific data to show its efficacy in growing hair and that it has a lower side effect profile compared to oral finasteride. Out of the 7 clinical studies reported above, only one study showed one event with sexual side effects (testicular pain). This is 1 out of 268 subjects in all of the studies, which equates to a rate of 0.37%. In contrast, oral finasteride is associated with sexual side effects in 1.8% to 3.8% of patients, which means that in the above 268 subjects, there should have been about 5 to 10 subjects experiencing some form of sexual side effects. However, this was not the case. Only 1 person had sexual side effects as opposed to 5 to 10 individuals. 

Pharmacokinetic studies by Caserini et al. suggest that lower doses of topical finasteride result in lower reduction of serum DHT compared to oral finasteride and thus lower sexual side effects. No study has conclusively shown the reason of how finasteride can cause sexual side effects. Certainly serum DHT is a contributing factor but may not be the only factor. The reason for this conclusion is because there are studies that patients were on high dosage of topical finasteride and still had no sexual side effects. 

In conclusion, the majority of studies on topical finasteride show no to only a few sexual side effects. However, this does not mean that sexual side effects can not happen. It just suggests that risk of sexual side effects are lower due to the fact that the finasteride is not taken orally. Additional larger clinical studies are needed to address the sexual side effects of topical finasteride. 

References:

1. Topical finasteride in the treatment of androgenic alopecia. Preliminary evaluations after a 16-month therapy course. GF Mazzarella, GF Loconsole, GA Cammisa, GM Mastrolonardo & Ga Vena; Pages 189-192 | Received 23 Aug 1996, Accepted 18 Mar 1997, Published online: 12 Jul 2009

2. Comparing the therapeutic effects of finasteride gel and tablet in treatment of the androgenetic alopecia. Hajheydari Z1, Akbari J, Saeedi M, Shokoohi L. .Indian J Dermatol Venereol Leprol. 2009 Jan-Feb;75(1):47-51.

3. Pilot Study of 15 Patients Receiving a New Treatment Regimen for Androgenic Alopecia: The Effects of Atopy on AGA. Rafi and Katz. SRN Dermatol. 2011;2011:241953. doi: 10.5402/2011/241953. Epub 2011 Apr 11.

4. Efficacy and safety of 3% minoxidil versus combined 3% minoxidil / 0.1% finasteride in male pattern hair loss: a randomized, double-blind, comparative study. Tanglertsampan C1. J Med Assoc Thai. 2012 Oct;95(10):1312-6.

5. A novel finasteride 0.25% topical solution for androgenetic alopecia: pharmacokinetics and effects on plasma androgen levels in healthy male volunteers. Caserini M, Radicioni M, Leuratti C, Annoni O, Palmieri R.  Int J Clin Pharmacol Ther. 2014 Oct;52(10):842-9. doi: 10.5414/CP202119.

6. Effects of a novel finasteride 0.25% topical solution on scalp and serum dihydrotestosterone in healthy men with androgenetic alopecia. Caserini M, Radicioni M, Leuratti C, Terragni E, Iorizzo M, Palmieri R. Int J Clin Pharmacol Ther. 2016 Jan;54(1):19-27. doi: 10.5414/CP202467.

7. Topical minoxidil fortified with finasteride: An account of maintenance of hair density after replacing oral finasteride. B. S. Chandrashekar, T. Nandhini, Vani Vasanth, Rashmi Sriram, and Shreya Navale. Indian Dermatol Online J. 2015 Jan-Feb; 6(1): 17–20. Doi: 10.4103/2229-5178.148925

8. A Systematic Review of Topical Finasteride in the Treatment of Androgenetic Alopecia in Men and Women. Sung Won Lee, MD,1 Margit Juhasz, MD,1 Pezhman Mobasher, MD,1 Chloe Ekelem, MD,1 and Natasha Atanaskova Mesinkovska, MD, PhD1. J Drugs Dermatol. 2018 Apr 1; 17(4): 457–463.

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