What “generic” means, legally, in the UK
A UK generic medicine must have the same active substance and pharmaceutical form as its reference medicine and must be shown to be bioequivalent. For standard bioequivalence studies, the 90% confidence interval for the ratio of key pharmacokinetic measures, usually AUC and Cmax, generally has to sit within 80.00% to 125.00%. That is a statistical acceptance range for the comparison, not a claim that each tablet can contain or deliver 80% to 125% of the branded dose.
This isn’t just a stated policy: published bioequivalence studies confirm both generic sildenafil and generic tadalafil meet this standard against their branded originals in practice, not just on paper.
Why prices differ so much
Once a drug’s patent expires, other manufacturers can produce approved generic versions without carrying the original development costs, and competition usually brings the price down. The active substance is the same, although packaging, appearance and inactive ingredients can differ between manufacturers.
An important honest caveat
The bioequivalence studies behind generic approval measure pharmacokinetics, how the drug is absorbed and processed by the body, not a head-to-head trial measuring erectile function scores between a specific branded and specific generic pill. It’s accurate to say generics are regulatorily required to match, and have been shown to match, brand bioavailability within tight, internationally defined limits. It would be an overclaim to say every generic has been separately proven identical in a real-world clinical outcomes trial against Viagra or Cialis by name, because that specific comparison usually isn’t what gets studied, bioequivalence is.
When branded might still make sense
For most people, an approved generic is expected to provide the same therapeutic effect as the reference product. A particular brand may still matter if someone needs a specific formulation, has an issue with an inactive ingredient, or benefits from consistent appearance and packaging. A pharmacist or prescriber can advise on those exceptions.
How UK clinics prescribe either option
Most branded and generic sildenafil and tadalafil products are prescription medicines and require a prescriber consultation. Viagra Connect 50mg and Cialis Together 10mg have Pharmacy medicine status, so a pharmacist may supply those specific products after checking your health history, current medicines and suitability. See our UK ED clinic comparison for current service and pricing information.