Tadalafil vs sildenafil: how the two labels compare

Tadalafil is the active ingredient in Cialis. Sildenafil is the active ingredient in Viagra. Both are PDE5 inhibitors, and both US labels list erectile dysfunction as a use.

Neither one produces an erection on its own; sexual stimulation is still needed. This is general label information, not personal medical advice.

In the shop, Apcalis-SX Oral Jelly 20 mg contains tadalafil, while Sidegra 100 and Malegra 100 contain sildenafil. The doses below come from the tablet labels. For any product, follow the leaflet in its own box.

The Cialis label also describes a once-daily regimen (starting at 2.5 mg), which is a different pattern from as-needed use. The Viagra label has no equivalent. Ask a doctor or pharmacist about it.

For Apcalis-SX jelly itself, follow the pack leaflet. The 20 mg figure comes from the top as-needed dose in the tadalafil label.

The Cialis label says that, taken as needed, tadalafil improved erectile function compared with placebo for up to 36 hours after dosing. Its mean half-life is 17.5 hours in healthy volunteers. These are trial findings, not a guarantee for any one person.

The Viagra label gives a half-life of about 4 hours.

On food, Cialis may be taken without regard to meals. Viagra can be taken with or without food, but after a high-fat meal absorption is slower, so it may take effect later than usual.

The main contraindications are the same:

• Anyone using a nitrate medicine in any form, such as a nitroglycerin tablet for chest pain. Blood pressure can fall sharply.
• Anyone using riociguat, a guanylate cyclase stimulator.
• Anyone allergic to the active ingredient or anything else in the product.

Both labels also advise caution with alpha-blockers and blood pressure medicines, which can lower blood pressure further. Tadalafil has its own cap when taken with strong CYP3A4 inhibitors such as ritonavir. Sildenafil's label suggests a lower starting dose with that group. Tell a doctor or pharmacist about everything you take.

Both list headache, indigestion, nasal congestion and flushing. What each label stresses differs:

• Tadalafil: back pain and muscle aches (myalgia), also pain in the limbs. The label says back pain or myalgia usually appears 12 to 24 hours after a dose and typically resolves within 48 hours.
• Sildenafil: flushing and visual changes such as a colour tinge or blurred vision, plus dizziness.

Not everyone gets these, and severity varies. If they bother you, speak to a doctor or pharmacist.

They are the same class of medicine. Both labels carry a warning on combining with other PDE5 inhibitors, saying safety and effectiveness of the combination have not been studied and it is not recommended.

Tadalafil stays in the body for a long time, so taking sildenafil on the same day means two medicines of one class acting together. Each label also caps use at once per day. The risks of low blood pressure and of an unusually long erection may rise. If you wonder about switching from one to the other, ask a doctor or pharmacist first rather than trying both in a row.

The urgent warnings are the same for both:

• An erection lasting more than 4 hours, or a painful one. Untreated, it can damage tissue permanently.
• Sudden vision loss in one eye, which the labels say can be a sign of NAION.
• Sudden hearing loss, with or without ringing or dizziness.
• Chest pain or worsening breathlessness.
• Allergic signs such as rash, swelling or trouble breathing.

Go to a hospital right away; do not wait for it to pass.

A label cannot answer that. It depends on your health conditions, your other medicines and how your body responds. Take it as a question for a doctor or pharmacist.

• Before starting, especially if you take chest-pain medicine, blood pressure medicine, antifungals or HIV medicines.
• If you have heart disease, low blood pressure, liver or kidney disease, or past eye problems.
• If side effects bother you, or you are unsure which ingredient or strength to choose.
• If you have any of the warning signs above: go to a hospital immediately.