Finasteride spray is a topical formulation used to treat male pattern hair loss by inhibiting the enzyme that converts testosterone to dihydrotestosterone (DHT). Whilst topical application aims to reduce systemic absorption compared to oral tablets, finasteride can still enter the bloodstream through the scalp. Sexual side effects, including erectile dysfunction, are recognised adverse reactions with oral finasteride, affecting approximately 2–4% of users in clinical trials. The risk with topical finasteride spray remains less clearly established, though systemic absorption does occur, meaning erectile dysfunction remains possible. This article examines the evidence, risk factors, and appropriate management strategies for men considering or using finasteride spray.

What Is Finasteride Spray and How Does It Work?

Finasteride spray represents a topical formulation of finasteride, a medication primarily used to treat male pattern hair loss (androgenetic alopecia) and benign prostatic hyperplasia. Unlike the conventional oral tablet form, topical finasteride is applied directly to the scalp with the intention of minimising systemic absorption whilst delivering the active ingredient to hair follicles.

The mechanism of action remains consistent across formulations: finasteride is a type II 5-alpha-reductase inhibitor. This enzyme converts testosterone into dihydrotestosterone (DHT), a more potent androgen responsible for miniaturising hair follicles in genetically susceptible individuals. By inhibiting this conversion, oral finasteride reduces scalp DHT levels by approximately 60–70%, with topical formulations generally showing more variable and potentially lower systemic effects.

Topical finasteride products may contain the active ingredient in various concentrations, often combined with other ingredients such as minoxidil or penetration enhancers. The rationale behind topical delivery is to achieve therapeutic effects locally whilst reducing systemic exposure and, theoretically, the risk of systemic side effects including sexual dysfunction.

It's important to note that while a topical finasteride cutaneous spray (Finjuve) has recently received UK marketing authorisation, most topical preparations are supplied as unlicensed 'specials' through private prescriptions. Oral finasteride (1mg tablets) has established marketing authorisation for male pattern baldness.

When using topical finasteride, proper application technique is essential. The product should be applied to a dry scalp and allowed to dry completely before contact with others, particularly women who are or may become pregnant, as finasteride can cause abnormalities in the male foetus.

Understanding the Risk of Sexual Side Effects

Sexual side effects, including erectile dysfunction (ED), decreased libido, and ejaculatory disorders, are recognised adverse reactions associated with oral finasteride. Clinical trials of oral finasteride 1mg reported sexual side effects in approximately 2–4% of men, compared to 1–2% in placebo groups, as documented in the Summary of Product Characteristics. These effects typically resolve upon discontinuation, though a small subset of patients report persistent symptoms.

The relationship between topical finasteride spray and erectile dysfunction remains less clearly established. Proponents of topical formulations suggest that reduced systemic absorption should theoretically lower the risk of sexual side effects. Some studies have demonstrated lower serum DHT reduction with topical application compared to oral administration, which may correlate with fewer systemic effects, though results vary between studies.

However, finasteride is lipophilic and can be absorbed through the scalp into systemic circulation. Research indicates that whilst topical application results in lower plasma finasteride concentrations than oral dosing, measurable systemic absorption does occur. Consequently, sexual side effects including erectile dysfunction remain possible with topical finasteride, though potentially at reduced frequency.

Several factors influence individual risk:

• Concentration and dosage: Higher concentrations may increase systemic absorption

• Application technique: Proper application to the scalp (rather than surrounding skin) may minimise absorption

• Individual variation: Genetic factors and baseline testosterone levels affect susceptibility

• Psychological factors: Anxiety about potential side effects may contribute to sexual dysfunction

The MHRA has highlighted that finasteride may be associated with depression, suicidal ideation and persistent sexual dysfunction in some cases. If you experience mood changes or sexual side effects, you should discuss these with your doctor promptly.

Currently, there is insufficient long-term data specifically examining erectile dysfunction rates with topical finasteride spray. Patients should report any suspected adverse reactions via the MHRA Yellow Card Scheme (yellowcard.mhra.gov.uk).

What to Do If You Experience Erectile Dysfunction

If you develop erectile dysfunction or other sexual side effects whilst using finasteride spray, several steps should be taken to address the situation appropriately and safely.

Immediate actions include:

• Do not abruptly panic: Sexual dysfunction can have multiple causes, and correlation does not always indicate causation

• Document symptoms: Keep a record of when symptoms began, their severity, and any other changes you've noticed

• Review other factors: Consider recent stress, relationship issues, other medications, alcohol consumption, or underlying health conditions that might contribute

Consult your GP or prescribing clinician promptly. A thorough assessment should include:

• Discussion of symptom onset and relationship to finasteride initiation

• Review of other medications and medical history

• Cardiovascular risk assessment (blood pressure, lipid profile)

• Evaluation for other causes of erectile dysfunction (diabetes, hypogonadism, psychological factors)

• Physical examination if clinically indicated

• Consideration of blood tests including morning testosterone (with repeat if low), HbA1c or fasting glucose, and prolactin if indicated

Your healthcare provider may recommend temporarily discontinuing finasteride spray to determine whether symptoms resolve. Sexual side effects associated with finasteride typically improve within weeks to months after stopping treatment, though individual experiences vary. In most cases, complete resolution occurs, though there have been reports of persistent symptoms in a small minority of patients.

If you experience mood changes, depression or suicidal thoughts while using finasteride, stop the medication and seek medical help immediately, as advised by the MHRA.

Referral to a specialist may be appropriate if you have suspected endocrine disorders, Peyronie's disease, treatment-refractory ED, or significant comorbidities.

Report any suspected adverse reactions to finasteride via the MHRA Yellow Card Scheme (yellowcard.mhra.gov.uk).

Alternatives and Treatment Options to Consider

For men concerned about sexual side effects from finasteride spray, several alternative approaches to managing hair loss exist, each with distinct mechanisms, evidence bases, and side effect profiles.

Topical minoxidil remains the only hair loss treatment licensed by the MHRA for both men and women. Available in 2% and 5% formulations, minoxidil works as a vasodilator and potassium channel opener, prolonging the anagen (growth) phase of hair follicles. It does not affect DHT levels and is not associated with sexual dysfunction. However, efficacy may be somewhat lower than finasteride for some patients, and continuous use is required to maintain results. Common side effects include scalp irritation and unwanted facial hair growth in some users.

Low-level laser therapy (LLLT) devices are CE/UKCA-marked medical devices registered with the MHRA for treating androgenetic alopecia. These use specific wavelengths of light to stimulate cellular activity in hair follicles. Evidence suggests modest improvements in hair density, though results vary considerably between individuals. LLLT carries minimal side effects but requires regular use and represents a significant financial investment.

Platelet-rich plasma (PRP) therapy involves injecting concentrated platelets from the patient's own blood into the scalp. NICE has not issued guidance recommending PRP for androgenetic alopecia, and evidence remains limited and heterogeneous. PRP is generally well-tolerated with minimal systemic effects.

Hair transplantation is a surgical option that relocates hair follicles from areas of good growth to thinning regions. This should be performed by regulated healthcare providers with appropriate surgical expertise.

Dutasteride, another 5-alpha-reductase inhibitor, blocks both type I and type II enzymes, achieving greater DHT suppression than finasteride. However, it is not licensed for hair loss in the UK and carries similar or potentially higher risks of sexual side effects.

For men experiencing erectile dysfunction related to finasteride, phosphodiesterase-5 (PDE5) inhibitors such as sildenafil may be considered if continuing finasteride is deemed important. These are contraindicated in patients taking nitrates or nicorandil, and cardiovascular assessment is necessary before prescribing. This approach should only be undertaken under medical supervision.

Ultimately, the decision regarding hair loss treatment should involve shared decision-making with your healthcare provider, weighing the psychological impact of hair loss against potential side effects, considering your individual risk factors, and establishing realistic expectations about treatment outcomes.

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