Finasteride for hair growth is an oral agent approved for the treatment of androgenetic alopecia in men.
Finasteride for hair was developed by the pharmaceutical company Merck and has been on the market in the USA since 1997 in a dosage of 1 milligram per tablet as a remedy for androgen-related hair loss. (In addition, finasteride is also prescribed in a dosage of 5 milligrams per tablet under the original brand name Proscar and other names to treat benign prostate enlargement).
When the patent protection for the active ingredient expired in October 2014, several products analogous to Propecia were launched, including the branded generics Finahair, Finapil and Finapuren. Many pharmaceutical manufacturers also offer generics with the active ingredient name Finasteride with the addition of 1 mg.
Finasteride: Who is it suitable for?
Finasteride for hair is recommended exclusively for men between the ages of 18 and 41 years, who show the first signs of androgenetic hair loss. The drug is not suitable for treating other forms of hair loss.
Finasteride for hair loss is not approved for use in women. For women of child-bearing age, the non-approval is based primarily on the risk for possible offspring, as finasteride interferes with the formation of the sexual organs in male foetuses, and on suspected influences on fertility. For post-menopausal women these restrictions do not apply. However, the usual dose of 1 mg a day for men proved to be ineffective in a study published in 2000 involving 137 women (the drug package leaflet refers to this study).  Later published studies with higher doses of finasteride (2.5 mg, 5 mg), on the other hand, reported clear treatment success  – so the final word on this topic is probably not yet spoken.
Use of finasteride
Finasteride for androgen-related hair loss is a small tablet to be taken once a day. No special accompanying measures are required; Finasteride can be taken with or without a meal.
To be effective, finasteride must be used continuously. A significant effect will only be seen after three to six months of regular use.
Mechanism and effectiveness of finasteride against hair loss
Finasteride for hair growth inhibits the enzyme 5α reductase, which converts testosterone into its active form dihydrotestosterone in many cells of the body. By lowering the level of DHT in the hair follicle, Finasteride interrupts the processes that lead to testosterone-dependent follicle miniaturization in androgenetic alopecia.
In most scientific and popular texts, Finasteride is said to act predominantly on the isoform II of 5α reductase. However, an in vitro study published in 2010 concluded that the substance inhibits the enzyme’s isoforms II and III. Both isoforms are found in different body tissues, with type III apparently occurring more frequently in the skin .
In the pivotal trials of finasteride for the treatment of androgenetic alopecia, 99% of the subjects had stabilised or improved after one year of regular use. In about 50% of the subjects, finasteride stimulated new hair growth.  Later large application studies confirmed or even exceeded these positive results  and demonstrated the continued efficacy of finasteride in long-term use .
Side effects of finasteride
Since finasteride for hair growth is taken orally, it must be expected that the substance also has effects in other body tissues. Wherever testosterone is converted into dihydrotestosterone by 5α reductase type II or III, finasteride interferes with the body’s own processes.
This said, the vast majority of users tolerate finasteride very well. The main side effects observed concern the sexual organs and well-being. The Propecia package leaflet states that the following side effects occur occasionally (in more than 0.1% and less than 1% of cases)
- decreased libido
- Erectile dysfunction and ejaculation disorders
If depression or sexual disorders occur in finasteride users, it is of course not easy to judge whether these problems are actually due to the use of the drug. Dramatic individual case reports do not help here, although they can draw attention to a potential problem. Information on the frequency of side effects must be based on studies in which large groups of finasteride users are compared with groups of non-users that are as similar as possible.
In a large study on the incidence of emotional side effects of finasteride (but in the 5 mg dose for the treatment of prostate hyperplasia), it was found that within 18 months, 1.95% of finasteride users experienced depression, while only 1.37% of non-users became depressed. The difference of 0.58% (i.e. almost 6 out of 1000 users) is now almost certainly attributable to Finasterid. In contrast, the suicide rate in the two groups was not significantly different .
However, the side effects of finasteride for hair can have a treacherous quality that does not occur with many drugs: in very rare cases, they apparently do not disappear when the drug is discontinued  (A similar situation is known from certain antidepressants – the serotonin reuptake inhibitors ). Between 1998 and 2013, the US Food and Drug Administration received 577 reports of persistent sexual dysfunction and 37 reports of suicidal behaviour (including 6 suicides) in men who had taken finasteride and stopped taking it after some time (however, many millions of men are likely to have used finasteride during this period)  After the FDA required the manufacturer of Propecia to list additional side effects on the package insert, the number of reports received increased significantly in the following years .
The symptoms, known as post-finasteride syndrome, include cognitive, emotional and sexual impairments that place a great deal of stress on those affected. The very rare Post-Finasteride Syndrome has been widely covered in the public media , but the specialist press was initially hesitant to address it . For a while there were certainly experts who questioned its existence – i.e. the connection between the symptoms that occurred and the intake of finasteride. In the meantime, no more doubts have been expressed; however, final clarity has not yet been achieved.
One way to avoid the systemic side effects of finasteride for hair growth would be to apply it locally. There are reports of first trials of finasteride solutions , solutions containing finasteride plus minoxidil, and nanoparticles filled with finasteride or dutasteride  . It is conceivable that in the future, local finasteride treatment of the scalp could minimize the risk of side effects of the treatment.