Finasteride is effective for prostate hyperplasia and baldness, but its side effects are one of the most debated topics in men's health medicine. The editors analyzed what the instructions and studies say about the frequency and nature of unwanted reactions.
General picture of security
Finasteride has been used for more than three decades, and its safety profile has been studied in tens of thousands of patients in randomized trials. Most people tolerate the drug well, but some men face side effects related to the mechanism of action — a decrease in dihydrotestosterone (DHT).
It is important to distinguish side effects by dosage. A dose of 5 mg for the treatment of prostatic hyperplasia is used in elderly men, who often have sexual dysfunction even without the drug. A dose of 1 mg for the treatment of baldness is prescribed for younger people, and here every side effect is perceived especially acutely.
A separate topic is reports of persistent symptoms that persist after discontinuation. They have been called "post-finasteride syndrome" and have become the subject of regulatory warnings, although the mechanism and frequency have not yet been established.
The editors consider the main groups of unwanted reactions, their frequency according to the instructions and research, as well as what should be done when they appear.
Sexual side effects
The most frequently discussed group is a decrease in libido, erectile dysfunction and ejaculation disorders, in particular, a decrease in the volume of ejaculate. DHT is involved in the regulation of these functions, so its decrease can disrupt them.
In 12-month trials of finasteride 1 mg for alopecia, any sexual side effect occurred in 3.8% of men versus 2.1% in the placebo group. So there is a difference, but the absolute additional risk is small.
The incidence is higher in men with BPH who received 5 mg. According to Proscar instructions, in the first year of the PLESS study, impotence was noted by 8.1% of patients versus 3.7% on placebo, decreased libido — 6.4% versus 3.4%, and decreased ejaculate volume — 3.7% versus 0.8%.
In most patients, these effects disappeared after the withdrawal of the drug, and in some - even against the background of continued treatment. However, there are reports of persistent symptoms, which will be discussed below.
| Adverse effect (year 1, PLESS) | Finasteride 5 mg | Placebo |
|---|---|---|
| Impotence | 8,1% | 3,7% |
| Decreased libido | 6,4% | 3,4% |
| Decrease in ejaculate volume | 3,7% | 0,8% |
Breasts, mood and other effects
A decrease in DHT and a moderate increase in testosterone, part of which is aromatized into estradiol, can change the androgen-estrogen balance in breast tissue. Therefore, side effects include soreness and enlargement of the mammary glands (gynecomastia), as well as isolated cases of breast cancer in men. Any lumps, discharge from the nipple, or pain require medical attention.
Depression and mood changes are listed in the instructions as possible side effects. In 2022, the FDA added information about suicidal ideation to Propecia's labeling based on post-marketing reports. A causal relationship has not been established, but patients and relatives are asked to pay attention to changes in mental status.
Other reactions include allergic manifestations (rash, itching, swelling of the lips and face), pain in the testicles, deterioration of sperm count and infertility, which have been reported in the post-marketing period.
Separately, we will mention the effect on PSA: the drug reduces its level by approximately half. This is not a side effect in the classical sense, but it must be taken into account in order not to miss prostate cancer.
- sexual: decreased libido, erectile dysfunction, decreased ejaculate;
- breast glands: tenderness, gynecomastia;
- mental: depressed mood, in rare reports - suicidal thoughts;
- allergic: rash, urticaria, angioedema;
- reproductive: testicular pain, deterioration of sperm quality.
Post-finasteride syndrome
This term describes persistent sexual, mental, and physical symptoms that patients report persisting for months and years after discontinuation. Among them are decreased libido, erectile dysfunction, decreased sensitivity, depression, and cognitive complaints.
Irwig and Kolukula (2011) described a group of young men in whom sexual dysfunction persisted for at least three months after discontinuation of the drug. Traish et al. (2011) in a review summarized the data on a persistent decrease in libido, erectile dysfunction and depression in some patients.
These works have limitations: small samples, lack of a control group, possible selection of patients with complaints. Therefore, the frequency of the syndrome is unknown, and its mechanism remains hypothetical — changes in neurosteroids and androgen receptor sensitivity are discussed.
Regulatory agencies, including the FDA, have included information on reports of persistent sexual dysfunction after withdrawal into the guidelines. This is not proof of causation, but an important signal to consider when discussing treatment with the patient.
What to do with side effects
First of all, don't hide your symptoms from your doctor. Many men are embarrassed to talk about sexual problems, but it is this information that determines whether to continue treatment.
The doctor can assess other causes of disorders (stress, vascular problems, other medications, hormonal abnormalities), discuss withdrawal or replacement of therapy. There are alternatives for alopecia, including topical treatments.
Mood changes, depression, thoughts of self-harm are a reason to seek immediate help, regardless of whether they are related to the drug.
Self-administration of finasteride without examination, especially on the background of other hormonal drugs, makes it difficult to recognize the cause of symptoms and increases the risk of missing a serious problem.
Editorial conclusion
Finasteride is well tolerated by most men, but sexual side effects are more common than with placebo, especially at the 5 mg dose in older adults. They are usually reversible.
The instructions also include warnings about gynecomastia, depression, suicidal thoughts and persistent sexual dysfunction after withdrawal. The latter remain the subject of research.
The decision on treatment should be made together with the doctor after discussing the expected benefits and possible risks.
Also read "Finasteride: mechanism of action", "Finasteride contraindications and interactions" and "Finasteride in the restoration of the hormonal system: what the research says".
References
- Merck Sharp & Dohme. Proscar (finasteride 5 mg) and Propecia (finasteride 1 mg): prescribing information. U.S. Food and Drug Administration.
- McConnell JD, Bruskewitz R, Walsh P, et al. The effect of finasteride on the risk of acute urinary retention and the need for surgical treatment among men with benign prostatic hyperplasia. N Engl J Med. 1998;338(9):557â563.
- Kaufman KD, Olsen EA, Whiting D, et al. Finasteride in the treatment of men with androgenetic alopecia. J Am Acad Dermatol. 1998;39(4 Pt 1):578â589.
- Irwig MS, Kolukula S. Persistent sexual side effects of finasteride for male pattern hair loss. J Sex Med. 2011;8(6):1747â1753.
- Traish AM, Hassani J, Guay AT, Zitzmann M, Hansen ML. Adverse side effects of 5α-reductase inhibitors therapy: persistent diminished libido and erectile dysfunction and depression in a subset of patients. J Sex Med. 2011;8(3):872â884.
- Thompson IM, Goodman PJ, Tangen CM, et al. The influence of finasteride on the development of prostate cancer. N Engl J Med. 2003;349(3):215â224.
- Gormley GJ, Stoner E, Bruskewitz RC, et al. The effect of finasteride in men with benign prostatic hyperplasia. N Engl J Med. 1992;327(17):1185â1191.
