Genuine sildenafil citrate from ADR Clinic, a regulated UK men’s health clinic
Sildenafil vs Viagra: What’s the Difference?
Sildenafil is the active ingredient in Viagra. When Pfizer’s patent expired in 2013, sildenafil became available as a generic medicine in the UK clinically identical, significantly cheaper.
What It Is
- Sildenafil citrate is the active ingredient in Viagra a prescription medicine licensed in the UK for adult men with erectile dysfunction.
How It Works
- A PDE5 inhibitor that increases blood flow to the penis during sexual stimulation. Onset: 30–60 minutes. Duration: up to 4 hours.
Who Can Take It
- Adult men diagnosed with erectile with erectile dysfunction, following an online consultation with a UK-registered prescriber.
WHAT IS VIAGRA SILDENAFIL CITRATE?
Sildenafil citrate is the active ingredient in Viagra the original erectile dysfunction medicine developed by Pfizer and first licensed in the UK in 1998. Pfizer’s patent expired in 2013, which means sildenafil citrate is now available in the UK both as branded Viagra and as generic sildenafil. Both are clinically identical: same active ingredient, same dosage strengths (25mg, 50mg, 100mg), same effect.
At ADR Clinic, sildenafil citrate is prescribed by UK-licensed doctors and dispensed through our GPhC-registered pharmacy partner. We supply MHRA-approved tablets only never grey-market imports.
Key facts about sildenafil citrate:
- Drug class: PDE5 inhibitor
- Available strengths: 25mg, 50mg, 100mg
- Onset of action: 30–60 minutes
- Duration of effect: up to 4 hours
- Available as: branded Viagra (Pfizer) or generic sildenafil
- Legal status in UK: Prescription-Only Medicine (POM), except Viagra Connect 50mg which is available over-the-counter after pharmacist consultation
How Sildenafil Citrate Works
Sildenafil citrate belongs to a class of medicines called phosphodiesterase type 5 (PDE5) inhibitors. During sexual stimulation, the body releases nitric oxide in the penis, which triggers a chemical called cGMP. cGMP relaxes the blood vessels and allows blood to flow in, producing an erection. PDE5 is the enzyme that breaks cGMP down when you have erectile dysfunction, PDE5 often breaks it down too quickly.
Sildenafil citrate blocks PDE5. This lets cGMP build up, blood flows freely, and an erection becomes possible but only when you’re sexually aroused. Sildenafil citrate does not cause an erection on its own; arousal is still required.
When to take it: 30 to 60 minutes before sexual activity.
With food: works fastest on an empty stomach. Heavy or fatty meals can delay onset by an hour or more.
With alcohol: small amounts are generally safe; heavy drinking reduces effectiveness.
Maximum frequency: once in any 24-hour period.
Sildenafil Citrate vs Branded Viagra: What’s the Difference?
Both products contain the same active ingredient sildenafil citrate. The clinical difference is zero. The cost difference is significant.
Feature
Active ingredient
Dosage strengths
Onset of action
Duration of effect
MHRA-approved
Prescription required
Typical UK private price
Manufacturer
Generic Sildenafil
Sildenafil citrate
25mg, 50mg, 100mg
30 – 60 minutes
Up to 4 hours
Yes
Yes*
From £ [X] per tablet
Multiple licensed UK
Viagra (Pfizer)
Sildenafil citrate
25mg, 50mg, 100mg
30 – 60 minutes
Up to 4 hours
Yes
Yes*
From £ [X] per tablet
Pfizer
Which should you choose?
- Choose generic sildenafil citrate if cost matters and you want the same clinical effect.
- Choose branded Viagra if you have a strong preference for the Pfizer original or have responded well to it previously.
Both are available through ADR Clinic following a free online consultation with a UK-registered doctor.
Sildenafil Citrate Dosages: 25mg, 50mg, 100mg Explained
Sildenafil citrate is available in three strengths.
Your prescriber will recommend a starting dose based on your medical history, age, and the severity of your symptoms.
Never adjust your dose without clinical advice.
Sildenafil 25mg
The lowest dose. Often prescribed for older men,
men taking certain blood
pressure medicines, or
those who experienced
side effects at 50mg.
From £ [X]/tablet
Sildenafil 50mg
The standard starting dose for most men new to ED treatment. Effective for the majority of patients.
Sildenafil 100mg
The maximum licensed dose. Used when 50mg has not been effective and is well-tolerated.
From £ [X]/tablet
All doses are reviewed and prescribed by GMC-registered UK doctors. Never take more than one tablet in 24 hours.
7 Reasons UK Men Choose ADR Clinic for Sildenafil Citrate
- GPhC-registered UK pharmacy – Every order of sildenafil citrate is dispensed legally under General Pharmaceutical Council oversight.
- GMC-registered UK prescribers – Your consultation is reviewed by a doctor on the General Medical Council register, never an algorithm or overseas pharmacist.
- Genuine MHRA-approved sildenafil citrate only – Sourced through regulated UK supply chains. We do not sell or import grey-market sildenafil from outside the UK.
- Free, confidential online consultation – Five minutes to complete, no upfront charge. You only pay if a prescription is approved.
- All three licensed strengths – 25mg, 50mg, and 100mg sildenafil citrate, prescribed at the dose clinically right for you.
- Discreet next-day delivery – Plain, signed-for packaging with no clinical markings. Free standard delivery on orders above £[X]
- Aftercare and dose adjustment – Your prescriber stays available for follow-up questions, dose changes, and ongoing support. No subscription required.
How to Get Sildenafil Citrate Online from ADR Clinic
Step 1 — Complete a free online consultation (5 minutes) Answer questions about your medical history, current medications, and ED symptoms. No payment at this stage.
Step 2 — UK doctor reviews your case A GMC-registered prescriber assesses whether sildenafil citrate is safe and appropriate for you.
Step 3 — Prescription issued (if clinically appropriate) If approved, your prescription is sent electronically to our partnered GPhC-registered pharmacy. If sildenafil citrate isn’t suitable, we’ll explain why and suggest alternatives like tadalafil or vardenafil.
Step 4 — Discreet next-day delivery Your sildenafil citrate is dispatched in plain, signed-for packaging — no clinical or pharmacy markings on the outside.
Is Sildenafil Safe? Who Should Not Take It
Sildenafil is one of the most extensively studied medicines in the world and is generally well-tolerated when prescribed appropriately.
Do not take sildenafil if you:
- Take nitrate medicines for chest pain (e.g. GTN, isosorbide)
- Take riociguat for pulmonary hypertension
- Have had a recent heart attack or stroke
- Have severe liver disease
- Have low blood pressure (below 90/50)
Speak to your prescriber before taking sildenafil if you:
- Take alpha-blockers for blood pressure or prostate symptoms
- Have a heart condition or angin
- Have sickle cell disease, leukaemia or myeloma
- Have a stomach ulcer or bleeding disorder
- Have an inherited eye condition (e.g. retinitis pigmentosa)
Common side effects (affect more than 1 in 100 people):
- Headache
- Flushing
- indigestion
- Blocked nose
- Dizziness,
- Visual disturbances.
Seek immediate medical help if you experience an erection lasting more than 4 hours (priapism), sudden vision loss, or chest pain.
What Our Patients Say About ADR Clinic
“Reviews coming soon — share your experience after treatment”
Genuine Sildenafil Online UK — Frequently Asked Questions
Yes. Sildenafil citrate is the active ingredient in Viagra. Branded Viagra is manufactured by Pfizer; generic sildenafil is manufactured by multiple licensed pharmaceutical companies. Both contain the same medicine at the same strengths and work in the same way.
No, they’re clinically identical. A 50mg generic sildenafil tablet has the same effect as a 50mg Pfizer Viagra tablet. Any perceived difference is usually placebo or formulation preference, not pharmacological strength.
Only Viagra Connect 50mg can be sold over the counter, and only after a pharmacist consultation. All other strengths of sildenafil citrate require a prescription. ADR Clinic provides this prescription through a free online consultation with a UK-registered doctor.
At ADR Clinic, sildenafil citrate starts from £[X] per tablet for the 50mg strength. Prices vary by dosage and pack size. The prescription itself is included — no separate prescription fee.
The NHS prescribes generic sildenafil citrate to men with specific medical conditions including diabetes, multiple sclerosis, prostate cancer, spinal injury, and after radical pelvic surgery. Most men who don’t meet these criteria use a private prescription through a regulated clinic like ADR Clinic.
Usually 30 to 60 minutes after taking it. It works fastest on an empty stomach. Heavy meals, especially fatty ones, can delay onset by an hour or more.
Up to 4 hours from the moment it starts working. You don’t have an erection for 4 hours- sildenafil citrate creates a 4-hour window during which arousal can produce an erection.
No. Sildenafil citrate is licensed for use as needed, no more than once in any 24-hour period. If you need daily ED treatment, tadalafil (Cialis) is usually a better option – your prescriber can advise.
The most common side effects are headache, facial flushing, indigestion, blocked or runny nose, dizziness, and visual disturbances such as blue tinge or light sensitivity. These are usually mild and resolve within a few hours. Rare but serious side effects include priapism (erection lasting over 4 hours), sudden vision loss, and sudden hearing loss – seek immediate medical help if these occur.
Do not take sildenafil citrate if you take nitrate medicines for chest pain, take riociguat for pulmonary hypertension, have had a recent heart attack or stroke, have severe liver disease, or have very low blood pressure. Always disclose your full medical history during your consultation.
Sildenafil citrate has been in clinical use since 1998 and is one of the most studied medicines in the world. Long-term use has not been linked to tolerance, dependence, or organ damage in healthy men. Annual prescriber review is recommended for men on ongoing treatment.
Orders approved before [time] are dispatched same-day for next-day signed-for delivery anywhere in the UK. Standard UK delivery is [free above £X / £X.XX flat].
About ADR Clinic + Clinical Governance
ADR Clinic is a UK-based men’s health clinic specialising in prescription erectile dysfunction treatment, including sildenafil citrate (Viagra).
We are committed to safe, evidence-based prescribing. Where sildenafil citrate is not clinically appropriate, our doctors will say so – and recommend alternatives or onward referral where needed.