Medicines form an essential part of the care provided by the NHS. More than one billion items are dispensed annually through community pharmacies, and the total bill for medicines is more than £17bn. For patients with long-term conditions such as diabetes, asthma or schizophrenia, daily medicines play a vital role in maintaining their health and wellbeing.

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We all know someone with a regular prescription, whether it’s for these illnesses, or for blood pressure, heart problems or cancer. Many of us have taken treatments for infections, or used creams for rashes and skin problems. Everyone takes it for granted that they will be able to get their medicines when they need them.

But everything we take for granted is at risk as a result of Brexit. If there isn’t a solid plan for managing supply, there could well be shortages. The challenges any plan must meet are enormous.

Let’s take a look at how medicines get from the factory to our local pharmacy. This is, by its nature, an international business. The active ingredients needed are often manufactured in India and the far east. These are then transported to manufacturing plants that turn them into the tablets and liquids that come in prescribed form. Many of the factories that supply the UK are elsewhere in Europe. From there, they are sent to wholesalers here who then distribute them to pharmacies and hospitals to be dispensed to patients. The entire process has to be carefully managed to ensure that everything happens in a timely way – particularly for medicines with short shelf lives, such as lifesaving EpiPens needed for those with severe allergies; or those with special requirements, such as insulin, which needs to be kept at between 2C and 8C at all times.

The goods that benefit from free movement across Europe include medicines. The pharmaceutical supply industry has adapted itself to these arrangements. So any big, sudden change, whether it’s leaving the customs union and single market, or negotiations breaking down resulting in no deal, has the potential to create major problems. Delays at ports, increased costs and legal or regulatory differences are among the issues.

Even as things stand, the process is a finely balanced one. At each step things can, and sometimes do, go wrong. For example, in preparing the active ingredient there can be contamination, which means the entire batch has to be discarded. At the manufacturing stage, there might be an issue that results in it failing quality control and then having to be discarded. During transport to the wholesaler, the container may become too hot and the contents exceed the maximum recommended temperature, after which it may have to be destroyed.

Any of these kinds of problems can lead to a delay in supply, and subsequent shortages of particular medicines. When this happens, as it does occasionally with a small number of medicines, the pharmacist may have to issue a shorter prescription in order to ensure the maximum number of patients have access to the available stock. If the supply issue persists, the pharmacist will either talk to the prescriber to find an alternative or ask the patient to go back to the prescriber.

At the moment, we can deal with these events. But they pale into insignificance compared to the problems Brexit has the potential to create.

Facebook Twitter Pinterest Border staff check lorries and trucks entering the UK at Portsmouth. Photograph: Matt Cardy/Getty Images

So what are the solutions? There is some manufacturing capacity in the UK but not nearly enough to meet the entire country’s demand for medicine. Trying to increase capacity can be done but would take a considerable amount of time, as any new facility needs to be approved for producing high-quality, safe medicines. Some, such as those that produce insulin, have very particular specifications. As a result, “just making more medicines here” cannot be the solution.

There is some discussion about stockpiling, but the immediate question is how could such vast quantities of drugs be stored in the appropriate environments (remember that some, for example, need to be kept cold)?

Then there is the issue of paying for the medicines. A stockpile lasting three months equates to around £4.5bn, which is an incredible amount of money. At the moment pharmacies don’t get paid until the medicines are dispensed. How could they afford to buy the amounts required? That’s before you even get to the question of shelf lives, which for some medicines are short.

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If the government and the NHS are serious about planning, then they must include community pharmacists who are used to dealing with these logistics and can support any decisions made. They are a critical part of the supply chain and are the final link to the patient. They may also have some capacity for storage – but there needs to be a clear understanding of what this capacity is, how it can be used and how medicines can be transferred between pharmacies in a timely and non-bureaucratic way. Not involving pharmacists could lead to poor decisions that will impact on patient safety and patient care.

Ultimately, we must remember that medicines are vital for the health and wellbeing of the population, particularly the most vulnerable members of society. Without timely access, yet more pressure will be placed on our hospitals through patients having crises due to a lack of medication.

No one wants this. Given the critical nature of medicines – and the understandable disquiet that millions of ordinary people who rely on prescriptions feel – clarity and engagement is vital. Government needs to reach out to pharmacies and suppliers and not bury its head in the sand. We are here, ready and eager to help secure the wellbeing of our patients. Hopefully that is a priority for those managing the Brexit process too.

Finally if you are a patient or a carer: hoarding medicines is never a good idea, as if your prescription changes, nothing you’ve stored at home can be reused and is wasted. Instead, talk to your pharmacist. Their aim is to do their best for you and those you care for. Getting frustrated with them will not help you or them – only by collaborating can we ensure we continue to meet everyone’s needs.

• Ash Soni is the president of the Royal Pharmaceutical Society