04/10/2013 09:04 BST | Updated 23/01/2014 18:58 GMT

Trust the Doctor, It's the Same Stuff

Patients across the country are increasingly being switched from familiar brand name medications that they have taken for years, to carbon copy medications known as generics. These generics are intended to contain the same active ingredients as the original drug with the same chemical structures and mode of action.

Typically the company that invents a drug is allowed to patent it and produce it exclusively for a period of ten to fifteen years, before any other company can copy it. This allows the pharmaceutical companies a chance to recoup the enormous investment costs of inventing new drugs. When a patent for a drug expires, the drug goes "off patent" and other companies can copy it. The most recent drug to go "off patent" was Pfizer's Viagra, which is now available as generic sildenafil.

Are these generic copies the same? Do they offer good value for money for the NHS and patients?

Copying drugs as complex as those available today is an incredibly difficult process. In a recent clinic, two patients prescribed generics gave me a good insight into how the public may view these copied drugs.

The first discussion was regarding the latest craze in technology, 3D printers. These amazing devices scan an item and then produce an exact three-dimensional copy of it. The dimensions and proportions of the copied item are exactly the same as the original. The patient in question pointed out that there are certain details that can't be carried across; the material used and the external colours. She noted that generics are packaged differently and the tablets themselves have different colours and coatings to the original drugs.

The second patient considered the matter like a cooking recipe. He had recently purchased Gordon Ramsay's latest cookbook. He therefore had the recipe to Mr Ramsay's flagship dish and the cooking instructions. However following these wouldn't make him a Michelin Star chef. As he pointed out, the dish might look and taste similar but it wouldn't be the same.

Fortunately the generics industry is a lot more sophisticated and produces copies of drugs that are incredibly similar to the originals. They will look different and have different outer packaging. The chemical ingredients, particularly the coatings, might not be exactly the same. However the active ingredient which makes the medicine work will be the same, and will have been proven to be the same before it is allowed on the market.

Is almost the same good enough? Do the differences that exist matter? We know from genetics that the 6 billion humans on the planet have DNA which is 99.9% identical. However we are all unique and we can see that even the smallest variations can lead to vast differences. When it comes to drugs, the mode of action is the most important factor. Generics have the same main ingredient and the same mode of action. To continue the cooking analogy, the proof is ultimately in the pudding. The truth is that the vast majority of generic drugs work for each patient in exactly the same way as the originals. They represent fantastic value for money for the patient and for the NHS. Often drugs that cost thirty pounds a month when patented can fall to as little as a pound a month when generic copies are produced. Generic Viagra (sildenafil) is now available at a fraction of the cost of the branded medicines helping the many thousands of people who cannot get these treatments on the NHS. The NHS does and must take full advantage of these falls. However, we occasionally see that the generic drug does not suit a particular patient or does not seem to work as well for a particular patient. For some this may be perception. For some this will be caused by a genuine difference in the way that their body responds to the medicine. As doctors we must accept that this does occur and work in the best interest of the patient. Ultimately the least useful medicine is the one that the patient does not take.