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 who 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.
Prostate cancer, urinary tract obstruction
Finasteride reduces total serum prostate specific antigen (PSA). In a typical patient undergoing treatment for BPH with finasteride (>= 6 months), a 50% decrease in serum PSA concentrations can be expected; however, individual patients may experience varying decreases in PSA values. During treatment, serum PSA concentrations may decrease even in the presence of prostate cancer. If clinicians use serum PSA concentrations as an aid in the detection of prostate cancer in men receiving finasteride, values should be doubled for comparison with normal ranges in untreated men. Any increase from baseline, even if the value is within the normal range for untreated men, may signal the presence of prostate cancer.
There is also an increased incidence of high-grade prostate cancer in patients receiving finasteride or dutasteride treatment. Results from the PCPT trial showed that men receiving finasteride had a 26% decreased risk of being diagnosed with prostate cancer when compared to placebo (p < 0.0001); however, the risk reduction was limited to Gleason score (GS) <= 6 cancers. There was an increased incidence of GS 8—10 prostate cancers with finasteride compared to placebo (1.8% vs. 1.1%, respectively). Therefore, in initiating or continuing treatment with finasteride, clinicians should weigh the known benefits of treatment against the potential risk and be aware that finasteride may increase the risk of high-grade prostate cancer. Further, lower urinary tract symptoms of BPH can be indicative of other urological diseases, including prostate cancer. Patients should be assessed to rule out other urological diseases prior to treatment with finasteride.
The clinical significance of finasteride’s effect on semen characteristics for an individual male patient’s fertility is not known; consider the potential effects on semen when assessing a male with infertility. Finasteride may cause spermatogenesis inhibition or oligospermia, decreased sperm motility, or decreased semen volume. One study showed a significant decrease in sperm count at 26 weeks, but not at 52 weeks. Semen volume and sperm concentration were also decreased, but this was not statistically significant. Sperm motility was decreased and it did reach statistical significance. During post marketing surveillance, male infertility and/or poor seminal quality following treatment discontinuation have been reported. It should be noted that normalization or improvement of seminal quality has also been reported after discontinuation of finasteride.
There are other side effects and they can reviewed here.
Are there any special groups?
Yes.Among the most significant are children and women.
Children: Finasteride cannot be used in children.
Women: Finasteride was termed 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.
Finasteride should be initiated with caution in patients with liver disease. Since finasteride is metabolized extensively in the liver, reduced metabolism is possible. The effect of liver impairment on finasteride pharmacokinetics has not been studied.
Clinical efficacy studies of finasteride for hair loss did not include subjects aged 65 and over. Based on the pharmacokinetics of finasteride 5 mg, no dosage adjustment is necessary in the geriatric patient. However, the efficacy of finasteride for hair loss in the elderly has not been established.
Men treated with finasteride should refrain from blood donation while taking finasteride. The purpose of this is to prevent administration of finasteride to a pregnant female transfusion recipient.
See here for other special groups, warnings, and precautions
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. Every overdose should be reported to your doctor.
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.
The above information is not comprehensive. For a complete list of side effects and contraindications to finasteride, please see the PDR.