Adverse event data

The table below shows the top 25 adverse events reported to the U.S. Food & Drug Administration (FDA) concerning finasteride used by younger men as a treatment for hair loss, from 2019–2021. The following filters were applied to minimize confounding factors:

Date first received by FDA: 2019–2021 / Sex: Male / Age: 18-40 / Suspected product: Finasteride only / Reason for use: Hair loss conditions only, excluding hair transplant / Concomitant products: None. Selected cases: 499 (17.5% of all finasteride-related cases during this time period). Median age: 28y. Submitted by: Consumer, 74.7%; Healthcare provider, 25.1%; Not specified: 0.2%.

Category of adverse events% of top 25 adverse events
Sexual anatomy & function
Erectile Dysfunction / Organic Erectile Dysfunction – 249
Loss Of Libido / Libido Decreased – 206
Testicular Pain – 61
Sexual Dysfunction – 45
Genital Hypoaesthesia [numbness] – 34
Ejaculation Disorder – 33
Penile Size Reduced – 30
40%
Neuropsychiatric domain
Depression / Depressed Mood – 188
Anxiety – 125
Suicidal Ideation – 103
Feeling Abnormal – 70
Anhedonia [inability to feel pleasure] – 39
Panic Attack – 38
34%
Cognition, memory & attention
Cognitive Disorder – 54
Amnesia – 38
Disturbance In Attention – 34
8%
Energy
Fatigue / Asthenia – 114
7%
Sleep
Insomnia / Sleep Disorder – 108
6%
Multi-system
Post 5-Alpha Reductase Inhibitor Syndrome – 57
3%
Sensory
Tinnitus – 38
2%
The number after each adverse event indicates the number of times it was reported in this filtered data set.

Explore and download the data (Airtable) ↗

Because 75% of these reports were submitted by Consumers, a separate analysis was done on reports submitted by healthcare providers. The composition of categories was similar, but there was a higher proportion of AEs in the neuropsychiatric category and a lower proportion in sexual anatomy & function:

Category% of top 25 adverse events
Neuropsychiatric domain41%
Sexual anatomy & function27%
Multi-system*8%
Sleep8%
Cognition, memory & attention5%
Energy (Fatigue)5%
Other (Dizziness & Headache)4%
Endocrine (Gynaecomastia)2%
Adverse events submitted by healthcare providers, 2019–2021 (see additional selection criteria above). * Post 5-Alpha Reductase Inhibitor Syndrome

See also: Adverse events affecting reproductive anatomy and sexual function, musculoskeletal adverse events, disability and deaths, and firsthand reports acquired by FOIA request.

Comparison to adverse events of minoxidil

Minoxidil is another treatment for hair loss used by younger men. It has a similar patient population as finasteride, but a different mechanism. A comparison of adverse events (AEs) of each drug can shed light on whether AEs might be attributable to the population or the drug.

Data for both drugs were filtered using the same criteria: Date first received by FDA: 2019–2021 / Sex: Male / Age: 18-40 / Suspected product: Minoxidil only or Finasteride only / Reason for use: hair loss conditions, excluding hair transplant / Concomitant products: None. Number of cases: Finasteride, 499; Minoxidil, 360.

Minoxidil AEs by category
Category% of top 25 AEs
Skin reactions45%
Incorrect use of product29%
Hair loss & drug ineffective14%
Headache & dizziness7%
Sexual dysfunction4%
Finasteride AEs by category
Category% of top 25 AEs
Sexual anatomy & function40%
Neuropsychiatric domain34%
Cognition, memory & attention8%
Energy7%
Sleep6%
Multi-system*3%
Sensory2%
* Post 5-Alpha Reductase Inhibitor Syndrome
Comparison

The only AE common to both drugs’ top 25 is Sexual Dysfunction:

FinasterideMinoxidil
Adverse event: Sexual Dysfunction2.7%2.6%
Category: Sexual anatomy & function40.0%4.4%
Treemaps

These figures show the category composition of the top 25 AEs of each drug.

Detailed data: Top 25 AEs of minoxidil and finasteride grouped by category
MinoxidilFinasteride
Skin reactions
Application Site Pruritus – 63
Application Site Pain – 29
Application Site Erythema – 27
Application Site Rash – 21
Application Site Dryness – 19
Pruritus – 16
Rash – 15
Application Site Exfoliation – 15
Application Site Irritation – 15
Dandruff – 12
Swelling Face – 11
Application Site Swelling – 11
Application Site Ulcer – 11

Incorrect use of product
Inappropriate Schedule Of Product Administration – 58
Incorrect Dose Administered – 26
Underdose – 25
Product Use In Unapproved Indication – 22
Overdose – 22
Product Administered At Inappropriate Site – 18

Hair loss & drug effectiveness
Alopecia – 57
Drug Ineffective – 25

Headache & dizziness
Headache – 24
Dizziness – 17

Sexual function
Erectile Dysfunction – 15
Loss Of Libido – 11
Sexual anatomy & function
Erectile Dysfunction / Organic Erectile Dysfunction – 249
Loss Of Libido / Libido Decreased – 206
Testicular Pain – 61
Sexual Dysfunction – 45
Genital Hypoaesthesia [numbness] – 34
Ejaculation Disorder – 33
Penile Size Reduced – 30

Neuropsychiatric domain
Depression / Depressed Mood – 188
Anxiety – 125
Suicidal Ideation – 103
Feeling Abnormal – 70
Anhedonia [inability to feel pleasure] – 39
Panic Attack – 38

Cognition, memory & attention
Cognitive Disorder – 54
Amnesia – 38
Disturbance In Attention – 34

Energy
Fatigue / Asthenia – 114

Sleep
Insomnia / Sleep Disorder – 108

Multi-system
Post 5-Alpha Reductase Inhibitor Syndrome – 57

Sensory
Tinnitus – 38