Medicines & Supplements A to Z > Sildenafil


Last updated on 14/07/2021.

Overview   |   Dosage   |    Side Effects   |   Precautions  |   Tips  |   Where To Buy  

GENERIC NAME: Sildenafil

CHINESE NAME: 西地那非、昔多芬

BRAND NAME(S) IN HONG KONG: Revatio 瑞肺得, Viagra 威而鋼, Tigerfil 喜健飛

DRUG CLASS: Antihypertensives, Vasodilators

SUB CLASS: Phosphodiesterase Inhibitors

USED FOR: Pulmonary arterial hypertension, Erectile dysfunction

AVAILABLE DOSAGE FORMS: 20 mg, 25 mg, 50 mg, 100 mg (tablets)

What is Sildenafil for?

Sildenafil belongs to a class of medications called phosphodiesterase inhibitors. Sildenafil (Revatio) is used to treat pulmonary arterial hypertension (high blood pressure in the lungs) by dilating blood vessels in the lungs to allow blood to flow easily. Sildenafil (Viagra) is used to treat erectile dysfunction (impotence) in men by increasing blood flow to the penis during sexual stimulation, which can cause an erection.

How to use it?

Sildenafil can be taken by mouth, with or without food.

Pulmonary arterial hypertension
5 mg or 20 mg three times daily.
Child over 1 year
Body weight >20 kg: 20 mg three times daily.
Body weight <20 kg: 10 mg three times daily.

Erectile dysfunction
50 mg approximately 1 hour before sexual intercourse, may adjust depending on response. Maximum dosage is 100 mg daily.

What are the side effects of Sildenafil?

Common side effects of Sildenafil include anemia, anxiety, diarrhea, dizziness, fluid retention, gastrointestinal discomfort, headache, insomnia and tremor.

Who should not take Sildenafil?

– People allergic to Sildenafil or any component of the formulation.
– Patients who are currently taking nitrates regularly or as emergency medication
– Patients who recently had myocardial infarction or stroke

Pharmacist Tips:

– This medication can make you dizzy. Avoid driving or operating machinery until you know how you respond to Sildenafil.
– Report to your doctor immediately if you experience sudden visual or hearing loss.
– If you are using Sildenafil for erectile dysfunction, seek medical assistance in case of prolonged erection (over 4 hours).
– Do not confuse Viagra (indicated for erectile dysfunction) with Revatio (indicated for pulmonary hypertension), which both contain Sildenafil.

Common dosing schedule:
For pulmonary hypertension, take Sildenafil three times daily.
For erectile dysfunction, take Sildenafil approximately 1 hour before sexual intercourse, but not more than once per day.

This schedule is for reference only, adjustments may be made according to individual needs.

Some common medications Sildenafil may interact with:
– Nitrates, e.g. Nitroglycerin, Nitric oxide, Isosorbide Mononitrate and Dinitrate
– Nicorandil

Please notify your doctor or pharmacist if you are taking the above medication, dosage adjustments might be needed.

Where to buy Sildenafil in Hong Kong?

In Hong Kong, Sildenafil is a prescription only medicine, and requires a prescription from a doctor to be purchased in a pharmacy. It can also be obtained from doctors. To find a pharmacy near you, refer to the list of pharmacies (“Authorized Sellers of Poisons”) from the Hong Kong Department of Health.

For more information about drug names and ingredients, you can visit Hong Kong’s Drug Office at

Need more information?

For detailed information about the use of Sildenafil in children, pregnancy and breastfeeding, and for questions about drug interactions, please check with your pharmacist or doctor.

Disclaimer: our goal is to provide you with the most relevant drug information and common dosage for Hong Kong. This information does not constitute medical advice. For specific treatment recommendations and advice, always discuss with your doctor or pharmacist, and follow the instructions included with your specific medicine.