Please read the full PDR for a full, detailed overview of finasteride.
Use of finasteride
Who can use finasteride and for what conditions?
Finasteride (1 mg) treats male pattern hair loss (MPB or androgenic alopecia) in men only. It has a proven effect on the crown. Its effectiveness in bitemporal recession has not been established.
In general, daily use for three months or more is necessary before benefit is observed. Continued use is recommended to sustain benefit, which should be re-evaluated periodically. Withdrawal of treatment leads to reversal of effect within 12 months.
Finasteride (5 mg) is used to treat men with symptoms of enlarged prostate to improve symptoms like difficulty urinating, to reduce the risk of getting urinary retention (urine trapped in the bladder), and to reduce the number of men who need surgery of the prostate.
Finasteride at any dose is not approved for the prevention of prostate cancer.
Who cannot take finasteride?
There is a very powerful warning about finasteride and the risk it poses for women who become pregnant or who breastfeed.
The following warning about women and finasteride cannot be overstated.
PREGNANCY: The PDR states, “Finasteride use is contraindicated in women when they are or may potentially be pregnant. Because of the ability of Type II 5α-reductase inhibitors to inhibit the conversion of testosterone to 5 α-dihydrotestosterone (DHT), finasteride may cause abnormalities of the external genitalia of a male fetus of a pregnant woman who receives finasteride. If this drug is used during pregnancy, or if pregnancy occurs while taking this drug, the pregnant woman should be apprised of the potential hazard to the male fetus.”
The PDR also states, “Women should not handle crushed or broken finasteride tablets when they are pregnant or may potentially be pregnant because of the possibility of absorption of finasteride and the subsequent potential risk to a male fetus. Finasteride tablets are coated and will prevent contact with the active ingredient during normal handling, provided that the tablets have not been broken or crushed.”
For this reason women should never use finasteride.
The medication has not been approved for use in children.
Children should not use finasteride and it should be kept far from their access (as should all medications).
Also, it should never be used in those allergic to any component of the finasteride tablet or medications in the same class of drug (e.g., dutasteride).
Possible side effects and reactions
Sexual side effects
Sexual side effects can include a decrease in sexual desire (libido), a decrease in semen volume, or erectile dysfunction (ED). These side effects were noted in 3.8% of men taking finasteride and in 2.1% of men taking a placebo (“sugar pill”). Breaking it down by each side effect, a decreased libido occurred in 1.8% of men (1.3% who took placebo), erectile dysfunction in 1.3% (.7% on placebo), and decreased semen volume in .8% (.4% who took placebo). A very small number of men experience other ejaculation disorders.
The PDR states, “Resolution occurred in men who discontinued therapy with finasteride tablets due to these side effects and in most of those who continued therapy. The incidence of each of the above adverse experiences decreased to <0.3% by the fifth year of treatment with finasteride tablets.”
This all sounds easy and straightforward – the sexual side effects are transient and manageable – but that is not the point. The point is that these side effects can happen. If you are one of the people that notices a change, the statistics about side effects occurring for a small number of patients won’t matter. Whether to continue the medication or not is an intensely personal choice. That is why it is so important to think about what it would mean if you were one of those few men who has an issue. A tiny decrease in semen volume may be trivial, but erectile dysfunction may not be, even if it goes away with time.
Lastly, there is the possibility a side effect can persist after the drug is stopped. It is rare, but possible. And again, “rare” is meaningless if it happens to you.
The studies quoted had very few men discontinue medication due to “drug-related sexual adverse experiences,” which was only 1.2% of men compared to .9% of men who took the sugar pill.
There have been rare reports of breast cancer in men. Some studies have shown breast cancer in men taking finasteride (about 1 in a thousand).
The PDR states that in a 7-year study of 18,882 men “there was 1 case of breast cancer in men treated with finasteride tablets, and 1 case of breast cancer in men treated with placebo.”
They noted, “The relationship between long-term use of finasteride and male breast neoplasia is currently unknown.”
Have any side effects been reported since finasteride was first approved?
These are called post marketing reports. Patients have the ability to report possible side effects voluntarily so a relationship to finasteride may not be established.
Some men have reported breast tenderness and enlargement.
There have been reports of “hypersensitivity reactions such as rash, pruritus, urticaria, and angioedema” (including swelling of the lips, tongue, throat, and face).
Sexual dysfunction that continued after discontinuation of treatment has also been noted. Reports include erectile dysfunction, libido disorders, ejaculation disorders, and orgasm disorders.
The PDR notes that testicular pain was reported.
The PDR states, “Treatment with PROSCAR for 24 weeks to evaluate semen parameters in healthy male volunteers revealed no clinically meaningful effects on sperm concentration, mobility, morphology, or pH. A 0.6 mL (22.1%) median decrease in ejaculate volume with a concomitant reduction in total sperm per ejaculate was observed. These parameters remained within the normal range and were reversible upon discontinuation of therapy with an average time to return to baseline of 84 weeks.
The PDR, in referring to post marketing reports, also states, “male infertility and/or poor seminal quality were reported rarely in men taking PROSCAR for the treatment of BPH. Normalization or improvement of poor seminal quality has been reported after discontinuation of finasteride. The independent role of PROSCAR in these events is unknown.”
Are there any special groups?
Children: Finasteride cannot be used in children.
Women: Finasteride is category X for a reason. It can lead to birth defects. Finasteride cannot be used in pregnant, possibly pregnant, or nursing women and should not be used in women at all. If a woman who is pregnant, is breastfeeding, or could possibly be pregnant, touches a tablet, she must wash her hands immediately with soap and water and contact her physician.
Elderly: Men aged 65 and over weren’t included in the early FDA studies on baldness, which used the low 1 mg dose of Finasteride. However, the PDR states, “Based on the pharmacokinetics (the way a drug behaves in the body) of finasteride 5 mg, no dosage adjustment is necessary in the elderly.”
Liver impairment: Since finasteride is metabolized in the liver, men with liver impairment may not be able to clear finasteride from the body as easily as men with normal livers.
Kidney impairment: No dosage adjustment is necessary.
Other warnings and precautions
Men using finasteride should not donate blood while on the medication or for one month afterward.
Prostate specific antigen
Prostate specific antigen is a blood test used to screen men for prostate cancer. The problem with finasteride is that it can make the PSA level very low in the men who take finasteride—even men with prostate cancer. This fact makes interpreting levels more difficult. A man with a normal level while on finasteride may still have prostate cancer. Interpreting levels must always be done with this knowledge. Every physician involved in your care must know you are on finasteride.
Also, any increases of PSA while on finasteride must be evaluated. The PDR states, “Any confirmed increase from the lowest PSA value while on finasteride tablets may signal the presence of prostate cancer and should be evaluated, even if PSA levels are still within the normal range for men not taking a 5 α-reductase inhibitor (e.g., finasteride).”
Increased risk of high-grade prostate cancer with finasteride and similar drugs
There is the possibility that finasteride may increase the number of men who eventually get high grade prostate cancer. In one study, men aged 55 and over with a normal digital rectal examination and normal PSA “taking finasteride 5 mg/day (5 times the dose of finasteride tablets used for hair loss)…had an increased risk” of higher grade prostate cancer. Some feel that the finasteride makes it easier to detect these higher grade cancers, but it is a risk that should be acknowledged.
The PDR does state, “Whether the effect of 5α-reductase inhibitors (like finasteride) to reduce prostate volume, or study-related factors, impacted the results of these studies has not been established.”
Is it possible to overdose on finasteride?
In clinical studies, single doses of finasteride up to 400x the dose given for hair loss and multiple doses of finasteride up to 80 g/day given for three months did not result in adverse reactions. At the moment, the PDR does not recommend any specific treatment for an overdose, though extremely high doses can kill rats.
Are there any drug interactions?
The PDR states, “No drug interactions of clinical importance have been identified.” Compounds that have been tested include antipyrine, digoxin, propranolol, theophylline, and warfarin and no clinically meaningful interactions were found.
Also, finasteride (1 mg or more), was used in studies with “acetaminophen, acetylsalicylic acid, α-blockers, analgesics, angiotensin-converting enzyme (ACE) inhibitors, anticonvulsants, benzodiazepines, beta blockers, calcium-channel blockers, cardiac nitrates, diuretics, H2 antagonists, HMG-CoA reductase inhibitors, prostaglandin synthetase inhibitors (also referred to as NSAIDs), and quinolone anti-infectives without evidence of clinically significant adverse interactions.”
This lack of effect on other medications and inability of other medications to affect a drug (finasteride) is exceedingly uncommon. Still, interactions that have yet to be identified are possible. Therefore, if any should occur report them to the FDA at 1–800–FDA–1088 or https://www.fda.gov/Safety/MedWatch/default.htm.