Hair Loss
Updated: Sep 28, 2022

Finasteride Interactions and Contraindications

Finasteride Interactions and Contraindications
Published: Feb 26, 2020

One of the most effective male pattern hair loss treatments of the last 3 decades is Propecia, often known by its generic name finasteride.  Finasteride is an oral medication designed to target the mechanism of male pattern hair loss at a chemical level, without the need for any messy creams or topical treatments, dubious devices or gimmicks, or any kind of hair replacement surgery.  Despite working systemically and altering certain hormone levels, finasteride is generally quite safe, with few side effects.  However, like any medication you take orally, there can be some finasteride interactions and contraindications that you should be aware of, which may mean finasteride is not the best choice for you as an individual. 

In this guide, we’ll explore the finasteride interactions and contraindications information, highlighting those conditions, medications, and other factors that might justify not choosing finasteride for your hair loss treatment.  The information is based on both clinical trials and independent studies and features conclusions from the sum total of information presented to the FDA on adverse drug interactions and side effects over the course of the nearly three decades that finasteride has been on the market.  This data bears out that, for most men seeking hair loss treatment, finasteride is safe and effective – and outlines the precautions for finasteride interactions, contraindications, and those who should not use finasteride. 

General Disclaimer

As with all of the medical articles and information we feature on Invigor Medical, it’s important to first provide a bit of a disclaimer.  This information is accurate and current to the best of our knowledge but is no substitute for a review of the official prescribing information for finasteride.  Additionally, it is no replacement for a frank and honest discussion with your doctor, or healthcare professional about the risks and benefits of starting hair loss treatment with finasteride.  Your prescriber can discuss finasteride side effects, finasteride interactions, contraindications, and other concerns, and help you decide if finasteride is the best choice for you.  Always review your complete medical history, any medical conditions, current medication, supplements, and herbal products you may be taking with your healthcare provider so that they can properly evaluate the suitability of finasteride or any other medication for your treatment plan. 

The Basics of Finasteride

Finasteride is usually supplied as a 1 mg pill, taken once daily orally, with or without food.  It’s a generic form of Propecia, which first came on the market in 1992, developed by Merck & Co.  It’s designed to treat male pattern hair loss/male pattern baldness, by addressing the underlying chemical triggers that cause male pattern hair loss in the first place. 

The substance that is implicated in hair loss – dihydrotestosterone, or DHT – is synthesized in the male body from testosterone, the male sex hormone.  Approximately 10% of testosterone in the body is converted to DHT, through a process carried out by an enzyme known as 5-alpha-reductase.  Finasteride acts as a 5-alpha-reductase inhibitor, dramatically reducing the conversion to DHT, and thus reducing the level of DHT in the body significantly (Marks, 2004).

Finasteride Interactions

Generally speaking, finasteride is considered safe for long-term use in males.  Like all medications, it does present some risk of side effects,  studies reveal that sexual adverse events occur at rates of 2.1% to 3.8%, erectile dysfunction is most common, followed by ejaculatory disorder and loss of libido. Additional side effects include a post-FDA approval finding that 5α-reductase Inhibitors increase the risk of high-grade prostate cancer, breast tenderness, and depression.

Aside from side effects, however, there are also some finasteride interactions that patients should be aware of, which may contraindicate use or require adjustment to dosage or treatment parameters.  Most of these finasteride interactions are a result of the way in which finasteride works in the body, and how it is metabolized and eliminated.

No Known Finasteride Interactions

The following clinical tests and studies have established no conclusive finasteride interactions with the following substances or bodily systems:

  • No specific finasteride interactions have been found within the cytochrome P450 route of drug metabolism, a common pathway by which drugs are broken down in the liver.  Tests with antipyrine, digoxin, propranolol, theophylline, and warfarin presented no significant finasteride interactions or adverse health outcomes.
  • Comprehensive finasteride interactions with a whole range of drugs in a clinical setting have not been conducted. Specific testing in clinical studies with the following medications did not find any finasteride interactions:
    • Acetaminophen
    • Acetylsalicylic acid (aspirin)
    • Alpha-blockers
    • Analgesics
    • Angiotensin-converting enzyme (ACE) inhibitors
    • Anticonvulsants
    • Benzodiazepines
    • Beta-blockers
    • Calcium-channel blockers
    • Cardiac nitrates
    • Diuretics
    • H2 agonists
    • HMG-CoA reductase inhibitors
    • Prostaglandin synthetase inhibitors (NSAIDs)
    • Quinolone anti-infective agents

Specific Finasteride Interactions, Adverse Events, and Precautions

Known finasteride interactions and adverse events/prohibitions on use in specific populations and those with certain conditions have been established, as outlined below.

  • Due to the mechanisms of action of finasteride, finasteride is not suitable nor approved for use in women.
  • Finasteride is not to be used by women who are pregnant or may become pregnant.  It should not be handled by women who are pregnant or may become pregnant, either.  The hormonal disruptions can cause birth defects and pregnancy complications, especially in male fetuses.
  • Once again, as finasteride is not suitable for use in women, especially pregnant women, it should not be taken by or handled by nursing mothers.
  • Finasteride is not suitable for use in children or pre-pubertal individuals.
  • Though specific testing on the use of finasteride and finasteride interactions and side effects was not conducted in elderly populations, there is no dosage adjustment or prohibition against use in men over age 65 – though its efficacy has not been firmly established.
  • The primary route of metabolism for finasteride in the liver.  Therefore, caution and/or dosage adjustment may be required in individuals with hepatic impairment or its use may be contraindicated entirely.
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Finasteride Contraindications

In addition to the finasteride interactions and prohibitions mentioned above, the formal contraindications for use of the drug, as established by the original approval for brand-name Propecia, include:

  • Pregnant women and those who may become pregnant should not use or handle finasteride.
  • Finasteride is contraindicated in patients with a known sensitivity or allergy to finasteride or any of its components.
  • Men who have or have had prostate cancer should talk to their doctor about the suitability of finasteride for hair loss treatment in their individual case.  Finasteride is known to cause an increased risk of high-grade prostate cancer in a small portion of individuals.

Other Considerations for Finasteride Interactions, Cautions, and Side Effects

The full range of finasteride interactions, cautions, contraindications, warnings, side effects, and similar information should be reviewed with your doctor or prescriber prior to starting a finasteride treatment regimen.  Every individual is unique, and a small portion of individuals may experience atypical symptoms, interactions, or responses to finasteride, as with any medication.  For more information, you can review the complete US prescribing information for brand-name Propecia, on file with the US Food and Drug Administration, via the following link:

Frequently Asked Questions

Should finasteride be taken at night?

There is no generally-accepted “best” time of day to take finasteride – you can take it at any time, once daily.  Finasteride can be taken with or without food.  You should, however, be consistent with your dosing time.  For example, if you choose to take it at night, you should take it at roughly the same time or period in your sleep/wake cycle each day. 

Does finasteride affect urination?

Finasteride is sometimes used for the treatment of an enlarged prostate, and the mechanism of action – even when being used for hair loss treatment – has the effect of somewhat decreasing the size of the male prostate.  Since prostates tend to enlarge with age and may place pressure on the bladder and urethra, increasing urination, treatment with finasteride does have the net effect of decreasing the frequency or urgency of urination in many men. 

Is finasteride safe for long-term use?

Finasteride is generally considered safe for long-term use.  While the aforementioned slight increase in the risk of high-grade prostate cancer has been established, the increased risk is fairly small (1.8% with finasteride vs. 1.1% with placebo), and has not deterred regulators or doctors from prescribing finasteride for hair loss treatment.  In fact, it is one of the top 100 most-prescribed medications within the US, with an estimated 10 million active prescriptions.  Long-term use is critical to realize the full effects of finasteride, as results often take several months to a year or more and hair regrowth is lost within 12 months of discontinuing the medication.

Concluding Thoughts

While finasteride is generally considered safe and is highly effective at stopping male pattern hair loss and even regrowing hair, proper precautions need to be taken before and during use of the drug.  Certain populations should avoid finasteride, as we outlined in our guide.  Finasteride interactions are fortunately few, and mostly relate to prohibited populations (women, pregnant women, children), and those with physical impairments (such as hepatic impairment) that can interfere with metabolism and elimination of the drug.  Generally speaking, there are no serious finasteride interactions with a range of medications tested during pre-marketing of the drug, nor adverse finasteride interactions that have come to light over nearly 30 years of use by millions of people.  For most men, it’s an affordable, effective, and safe way to reverse the effects of male pattern hair loss. 

ALSO READ – An Overview of Finasteride Side Effects


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Written by Riazzudin


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