What Is a Generic Medicine? Generic vs Branded Medicines, Explained (UK)

By Matt Brindley. For UK adults. Reviewed November 2026.

You've almost certainly taken a generic medicine already.

The paracetamol in your kitchen cupboard? Probably a generic. Same medicine as the branded box next to it on the shelf... just a fraction of the price.

So what's the difference? And why does it matter?

In short

• A generic medicine has the same active ingredient and the same clinical effect as the branded version [1].
• Same standards. In the UK, generics must meet the same safety and quality requirements as the original branded medicine [2].
• It's all about the patent. A new medicine is protected by a patent, usually for up to 20 years [3]. Once that protection ends, other companies can make it, and that's when generics appear.
• That's why they're cheaper. The company that invented the medicine has the research costs to recover. Generic makers don't, so generics can cost up to 95% less [1].
• The Prozac test. In England, fluoxetine was prescribed 7,573,765 times in a year. Only 39 of those were written as Prozac [18].
• Naltrexone is available as a generic. The medicine is the same whichever box it comes in. What makes the difference is how it's used.

What is a generic medicine?

Every medicine has two names.

The generic name is the active ingredient: the part that does the work.

The brand name is the one a company gives its version.

You know these already:

A box of supermarket paracetamol and a box of Panadol contain the same active ingredient. NHS guidance is clear that generic and branded medicines "have the same active ingredient and the same clinical effect" [1].

Why are new medicines so expensive?

Because inventing one takes a long time, and a lot of money.

It typically takes 10 to 15 years to discover, develop and test a new medicine, and it typically costs more than £1 billion, though estimates vary [4]. That covers the research, the staff, the materials, and years of clinical trials to prove it's safe and that it works.

So the company protects its invention with a patent.

What does a patent do?

A patent stops anyone else making and selling the medicine without the patent owner's permission. That gives the company time to recover what it spent, and make a profit.

In the UK, a patent lasts up to 20 years from the date it was applied for [3]. The owner has to pay a renewal fee every year to keep it going. If they stop paying, the patent ends early [3].

Medicines can get a little extra time. Because the years spent getting a licence eat into the patent, a medicine can get a supplementary protection certificate, which adds up to five more years [5].

What a patent can't do is go on forever.

So when does a medicine become "generic"?

When the protection ends, because the patent has run its full term or it has lapsed.

From that point, other companies can make the same medicine. They still have to get it licensed in the UK, and meet the same quality and safety standards [2]. But they haven't had to pay for the original research, and they're competing with each other on price.

That's why generics can cost up to 95% less [1], and why the NHS uses them wherever it can. The money saved pays for more treatment [1].

The stories behind the brands you know

Every famous medicine brand started as somebody's invention. Here's what happened to four of them.

Panadol and Calpol (paracetamol)
Paracetamol was first made in 1877 [7]. For decades it was largely ignored, because a related medicine, phenacetin, was thought to be safer. Then, in the 1940s, researchers found the body turns phenacetin into paracetamol anyway [7]. In 1955, Panadol was launched as the first paracetamol-only painkiller [8]. Calpol followed in 1959, made by Calmic Ltd of Crewe [9]. Two famous boxes. One medicine inside both.

Nurofen (ibuprofen)
Ibuprofen is British. A Boots team in Nottingham, including Stewart Adams and John Nicholson, first made it in December 1961, and it was patented in 1962 [10]. It became a prescription medicine in the UK in 1969, and in 1983 it went on sale over the counter as Nurofen [10]. Adams later admitted that in Moscow in 1971, with a hangover from vodka toasts the night before an important speech, he took a dose himself [11]. Today ibuprofen is made by many companies, and supermarket ibuprofen sits next to Nurofen on the shelf.

Aspirin and Disprin
"Aspirin" was a brand name. Bayer made the medicine in Germany in 1897 and registered the trademark in 1899 [12]. After the First World War, the trademark was taken away in many countries, including the UK [12][13]. That's why, in the UK, "aspirin" is now simply the name of the medicine. In 1948, Reckitt and Colman in Hull launched Disprin, a soluble aspirin [14]. A brand that turned into the generic name itself.

Prozac (fluoxetine)
Prozac became a household name. Scientists at Eli Lilly found fluoxetine in 1972 [15]. It arrived in Britain in 1989, and within a year it was already making headlines [16]. In January 2000, its patents ran out in several European countries, and the first UK generic went on sale within days [17].

Fast forward to today.

In the 12 months to August 2026, prescribers in England wrote 7,573,765 prescription items for fluoxetine. Just 39 of them were written as Prozac [18].

That's about one in every 194,000.

Same active ingredient. The brand people remember. The generic almost everyone gets.

And naltrexone's story?

Naltrexone was invented in the US in the 1960s. The patent was filed in 1963 and granted in 1967, to a company called Endo Laboratories [19].

Here's the twist. It took until November 1984 for naltrexone to be approved in the US, to help treat opioid addiction [20]. Under US rules at the time, a patent lasted 17 years from the date it was granted. So the patent ran out in the same year the medicine was first approved [19].

It was approved in the US to treat alcohol dependence in 1994 [21]. Meanwhile, in Finland, a researcher called Dr John David Sinclair was studying something different: what happens when you take it before drinking, rather than instead of drinking. That work became The Sinclair Method [22].

Today, naltrexone is a low-cost generic medicine. In England, about 99% of naltrexone prescriptions are written under its generic name [18]. (Those figures cover every use of naltrexone, not only alcohol.)

Are generic medicines as good as branded ones?

Yes.

In the UK, there are strict quality controls before any medicine can be made available, and generics must meet the same safety and quality requirements as the original branded product [2].

"Generic" describes the name and the price. Not the quality.

Why does my prescription say a different name?

Prescribers are encouraged to prescribe by the generic name, and the NHS aims to use generics where it can [1].

The generic name is always on the packet somewhere, even when a brand name is bigger [2]. If anything about your medicine looks different from last time, ask your pharmacist. That's exactly what they're there for.

What about naltrexone?

Naltrexone has been around for a long time, and it's available in the UK as a generic medicine, under its generic name, naltrexone hydrochloride [6].

Here's the important bit.

The medicine is the same whichever box it comes in. What changes the experience is how it's used.

The usual UK way is daily, once you've stopped drinking. The Sinclair Method uses the same medicine only on days you plan to drink, before drinking, to drink less over time. That second way is off-label: What does off-label mean?

More on the two ways: Should naltrexone be taken daily or before drinking?

Common questions

Is a generic medicine the same as the branded one?
Yes. Same active ingredient, same clinical effect, same quality standards [1][2].

Why are generic medicines cheaper?
Because the original company's patent has ended. Generic makers didn't pay for the years of research and trials, and they compete with each other on price [1][3].

How long does a medicine patent last?
In the UK, up to 20 years from the date it was applied for, if the renewal fees are paid every year [3]. Medicines can get up to five more years through a supplementary protection certificate [5].

Is fluoxetine the same as Prozac?
Yes. Fluoxetine is the active ingredient in Prozac. Since the patents ended, other companies make it too, and in England almost every prescription is now written as fluoxetine [18].

Is generic naltrexone the same as branded naltrexone?
Yes. Same active ingredient, made to the same standards [1][2].

Where can I get naltrexone safely?
Naltrexone is a prescription-only medicine. Here's how to get it safely in the UK: Where to buy naltrexone in the UK

If you'd like support from us

Rethink Drink is a UK coaching service built around The Sinclair Method. Our programmes include a consultation with an independent prescriber, who decides whether treatment is suitable. Clinical oversight is provided by consultant psychiatrist Professor Jonathan Chick. Any prescription is dispensed by an independent partner pharmacy. Our coaches work with you, week by week, on everything around it.

And whatever happens, you can talk to someone today. Drinkline, the national alcohol helpline, is free and confidential: 0300 123 1110.

Please look after yourself

Before you change how much you drink or start any medication, speak to your GP or a prescriber.

I really hope this post helps. If you have any questions, you can contact me here.

Matt

Sources

1. West Suffolk NHS Foundation Trust. Generic and branded medicines: general information (patient leaflet). https://www.wsh.nhs.uk/CMS-Documents/Patient-leaflets/PharmacyServices/6681-1-Generic-and-branded-medicines-general-information.pdf
2. Powys Teaching Health Board (NHS Wales). Brand to generic medication information. https://pthb.nhs.wales/services/pharmacy-and-medicines-management/public/brand-to-generic-medication-information/
3. UK Intellectual Property Office. Manual of Patent Practice, section 25: term of patent. https://www.gov.uk/guidance/manual-of-patent-practice-mopp/section-25-term-of-patent
4. ABPI (Association of the British Pharmaceutical Industry). Making medicines. https://www.abpischools.org.uk/topics/making-medicines/
5. nibusinessinfo.co.uk (Invest NI). Supplementary protection certificates. https://www.nibusinessinfo.co.uk/content/supplementary-protection-certificates
6. BNF (British National Formulary). Naltrexone hydrochloride. https://bnf.nice.org.uk/drugs/naltrexone-hydrochloride/
7. University of Bristol, School of Chemistry. Paracetamol: history. https://www.chm.bris.ac.uk/motm/paracetamol/paracetamolh.htm
8. Haleon. Our history (Panadol, 1955). https://haleon.com/who-we-are/history
9. List of paracetamol brand names (Calpol: Calmic Ltd, Crewe, 1959; cites The Guardian, 2019). https://en.wikipedia.org/wiki/List_of_paracetamol_brand_names
10. Stewart Adams (chemist). https://en.wikipedia.org/wiki/Stewart_Adams_(chemist) ; Royal Society of Chemistry, ibuprofen chemical landmark (2013). http://www.rsc.org/AboutUs/News/PressReleases/2013/ibuprofen-chemical-landmark.asp
11. Smithsonian Magazine. The inventor of ibuprofen tested the drug on his own hangover. https://www.smithsonianmag.com/innovation/inventor-ibuprofen-tested-drug-his-own-hangover-180975088/
12. German Patent and Trade Mark Office (DPMA). Brands with history: Aspirin. https://dpma.de/english/our_office/publications/milestones/brandswithhistory/aspirin/index.html
13. IP Digit (summarising the Financial Times). Bayer's Aspirin: a lasting success without patent and trademark protection. https://ipdigit.eu/2011/10/bayers-aspirin-a-lasting-success-without-patent-and-trademark-protection
14. Museums Victoria. Disprin (Reckitt and Colman, launched November 1948). https://collections.museumsvictoria.com.au/items/1560911
15. EBSCO Research Starters. FDA approves Prozac as an antidepressant. https://www.ebsco.com/research-starters/health-and-medicine/fda-approves-prozac-antidepressant
16. Drug and Therapeutics Bulletin (BMJ), 1990;28(9):33, on fluoxetine (Prozac). https://dtb.bmj.com/content/28/9/33
17. The Pharma Letter. Bioglan launches first generic Prozac (11 January 2000). https://www.thepharmaletter.com/bioglan-launches-first-generic-prozac
18. OpenPrescribing.net (Bennett Institute, University of Oxford), NHS England prescribing data, September 2025 to August 2026, accessed 5 November 2026. Fluoxetine hydrochloride (BNF 0403030E0): 7,573,765 items; Prozac (0403030E0BB): 39 items. Naltrexone hydrochloride (0410030E0): 20,077 items, of which generic (0410030E0AA) 19,864. https://openprescribing.net/chemical/0403030E0/
19. US Patent 3,332,950 (Blumberg, Pachter and Matossian; Endo Laboratories; filed 1963, granted 25 July 1967). https://patents.google.com/patent/US3332950
20. Journal of Substance Abuse Treatment, 1985;2(2):117-22, "Naltrexone": approved by the FDA in November 1984 as an adjunct in the treatment of opioid addiction. https://pubmed.ncbi.nlm.nih.gov/3007777
21. SAMHSA, TIP 49, Incorporating Alcohol Pharmacotherapies Into Medical Practice (2009), chapter 4: FDA approval for alcohol dependence, 1994. https://www.ncbi.nlm.nih.gov/books/NBK64042/
22. Sinclair JD. Evidence about the use of naltrexone and for different ways of using it in the treatment of alcoholism. Alcohol and Alcoholism, 2001. https://cthreefoundation.org/wp-content/uploads/2018/08/review_nal_2001_print_us_1.pdf