Sildenafil vs Tadalafil: Comparing ED Medications in Australia

Erectile dysfunction (ED) affects approximately one in five Australian men over 40, with prevalence increasing significantly with age. The Australian Institute of Health and Welfare (AIHW) estimates that ED affects a substantial proportion of men in older age groups, with the majority of cases having a primarily vascular or neurogenic basis. Sildenafil and tadalafil are both phosphodiesterase type 5 (PDE5) inhibitors -- recommended as first-line pharmacological treatment by the Australian Therapeutic Guidelines (eTG) -- but they differ meaningfully in duration, timing requirements, side-effect profile, and practical use.

During sexual arousal, nitric oxide is released in penile tissue, triggering production of cyclic GMP (cGMP). cGMP relaxes smooth muscle and increases blood flow, producing an erection. PDE5 is the enzyme that breaks down cGMP. By inhibiting PDE5, sildenafil and tadalafil allow cGMP to accumulate and sustain the erection for longer. Neither drug produces an erection without arousal -- sexual stimulation is still required.

Sildenafil was the first oral ED medication approved in Australia (TGA approval 1998). Available as generic tablets in 25mg, 50mg, and 100mg doses. The typical starting dose is 50mg, taken approximately 30-60 minutes before sexual activity, not more than once per day.

When sildenafil works well:

• You prefer to take medication only when needed and can plan around a 30-60 minute onset window
• You want a shorter duration of action (some men prefer the effect to be time-limited)
• Cost is a priority -- generic sildenafil is typically the lowest-cost PDE5 option

Key clinical considerations:

• High-fat meals can delay absorption by up to an hour and reduce peak plasma concentration -- the eTG recommends taking sildenafil on an empty stomach or after a light meal
• The 4-6 hour window means dose timing matters; taking it too early may allow the effect to fade before it is needed
• Sildenafil mildly inhibits PDE6 in the retina, which can cause visual disturbances (blue tinge, increased light sensitivity) in approximately 3% of users -- an effect not seen with tadalafil
• Common side effects (from phase III trial data): headache (16%), flushing (10%), nasal congestion (4%), visual disturbance (3%)

Tadalafil (TGA approval 2003) has a plasma half-life of approximately 17.5 hours -- roughly four times longer than sildenafil's 4-hour half-life. This produces a window of action up to 36 hours for as-needed dosing, and continuous coverage with daily 5mg dosing.

As-needed dosing (10mg or 20mg):

• Onset similar to sildenafil (30-60 minutes), but the window extends up to 36 hours
• Minimal food effect -- can be taken with or without meals
• Provides flexibility for men who prefer not to time the dose around a meal or a precise activity window

Daily low-dose (5mg):

• After approximately 5 days of daily dosing, steady-state plasma levels are achieved
• Completely eliminates the need to plan timing -- spontaneity is fully preserved
• TGA-approved for benign prostatic hyperplasia (BPH), making it a useful option for men with both ED and lower urinary tract symptoms

Key clinical considerations:

• Common side effects: headache (15%), dyspepsia (10%), back pain and myalgia (muscle aches) -- these are specific to tadalafil and typically occur 12-24 hours after a dose, resolving within 48 hours
• No visual side effects (tadalafil does not inhibit PDE6)
• Daily dosing has a higher monthly cost but may be preferred by men who are sexually active multiple times per week

Neither sildenafil nor tadalafil is PBS-listed for erectile dysfunction, so both are dispensed as private (non-PBS) prescriptions and the cost is not government-subsidised. Generic versions are bioequivalent to the original branded products (Viagra, Cialis) under TGA requirements and are substantially less expensive than the branded originals. Prices vary between pharmacies and by dose and quantity, so ask your pharmacist for the generic option and the price of the exact item dispensed.

Other contraindications and cautions (per eTG and TGA product information):

• Recent myocardial infarction or stroke (within 3-6 months) -- requires cardiology input before PDE5 use
• Unstable angina or heart failure with reduced ejection fraction
• Systolic blood pressure below 90 mmHg
• Severe hepatic impairment
• Concurrent alpha-blockers for BPH -- can cause postural hypotension; start with the lowest PDE5 dose and allow at least 4 hours between alpha-blocker and PDE5 doses
• Retinitis pigmentosa (sildenafil only -- avoid due to PDE6 retinal effect)

There is no universally "better" option. The choice depends on sexual activity frequency, whether you have concurrent BPH, side-effect tolerance, and cost preference.

If one PDE5 inhibitor is ineffective or causes unacceptable side effects, switching to the other is a standard clinical approach. The eTG recommends trying a PDE5 inhibitor on at least 4-6 separate occasions before concluding it is ineffective -- the first attempt is often not representative (performance anxiety, incorrect timing, heavy meal).

When switching from as-needed tadalafil to sildenafil, allow at least 48 hours for washout. After sildenafil, 24 hours is adequate before starting tadalafil.

Both sildenafil and tadalafil are Schedule 4 (prescription-only) medications. A structured telehealth consultation is appropriate for ED prescribing when the doctor can adequately assess cardiovascular risk, current medications, and contraindications -- including a validated IIEF-5 (International Index of Erectile Function) questionnaire to characterise the severity and likely aetiology of ED.

A few practical points help these medicines work as intended:

• Alcohol. A small amount is usually fine, but heavier drinking can both worsen erectile function and add to the blood-pressure-lowering effect of PDE5 inhibitors, increasing the chance of dizziness or headache. It can also make the medicine seem not to work.
• Food. Sildenafil is more affected by food than tadalafil. A heavy, fatty meal can delay its onset and reduce its effect, which is why it is often taken on a relatively empty stomach. Tadalafil is largely unaffected by food.
• Timing. Sildenafil needs to be taken ahead of activity within its shorter window, while tadalafil's longer duration removes much of the timing pressure. Neither produces an erection without sexual stimulation.
• First attempts. It is common for a first try to be disappointing because of anxiety, incorrect timing, or a heavy meal. Guidelines suggest trying a medicine on several separate occasions before concluding it does not suit you.

Choosing between sildenafil and tadalafil is only part of the picture. Because the most common cause of erectile dysfunction is vascular, a new or worsening erection problem can be an early signal about heart and blood-vessel health, and it is worth having that reviewed rather than treated in isolation. Managing blood pressure, cholesterol, blood sugar, weight, smoking, and physical activity improves erectile function and overall health at the same time. Our guide on erectile dysfunction causes, options, and assessment covers how a safe assessment looks at these factors before any medication is considered.

• Healthy Male (Andrology Australia): erectile dysfunction
• Australian Prescriber: management of erectile dysfunction
• Healthdirect: erectile dysfunction
• Medical Board of Australia: telehealth consultations with patients
• TGA: Poisons Standard and prescription (Schedule 4) medicines