If you went to see your GP 20 years ago, chances are you'd leave with a prescription for antibiotics or an inhaler. Today heart and blood pressure drugs are the most prescribed medicines in most parts of the UK – with one in four people over the age of 40 on statins, drugs to lower cholesterol. Meanwhile, Levothyroxine, medication for thyroid disease, has leapt from number 18 to the third most dispensed drug in England. So what has changed? Is heart disease more common and does no one get asthma any more? And what can doctors' prescription pads from 20 years ago tell us about our health today – and the way doctors are treating us?

Statins

Twenty years ago, the most dispensed drug in England was the asthma inhaler, salbutamol. The latest statistics show that the statin simvastatin has now replaced it at the top of the most dispensed drugs list. Salbutamol inhalers are down to number seven, despite the fact over a million more people use them today.

The reason is that in the 90s, when statins were first introduced, they were only given to patients with very high cholesterol levels. Today they are standard treatment for anyone who has had a heart attack and are often started in patients with much lower cholesterol levels than previously.

Dr Richard Lehman, an Oxfordshire GP of 31 years, feels NHS suggestions that "one in four adults over 40 should be taking statins" are to blame: "I'm not sure the public's preoccupations with health have changed that much but doctors' target-centred thinking has – hence the enormous increase in prescription of statins."

But, says Scottish GP Dr Steve McCabe, "Statins – for all the potential problems with undesirable side effects – remain one of the most significant developments of the last 20 years. Since they were introduced, our rates of things such as heart attacks has plummeted."

Antibiotics

Other differences are down to new medicines. "Have we got better drugs now? Are they more effective? Yes on both counts," says Dr Domhnall MacAuley, a Belfast GP. He gives the example of drugs to prevent stomach ulcers, which appear to be replacing antibiotics on the list.

Once the second most dispensed drug type in England, antibiotics are now only the 14th. In light of increasing resistance and "superbugs", says MacAuley, "Current evidence is in favour of a less absolute approach to prescribing antibiotics."

Paracetamol

Dr Lehman says that hard cash has also always played a part in which medicines are prescribed. "Cost was a major factor in our thinking then, as now." Yet while today's doctors have to keep an eye on budgets, 20 years ago it was the cost to patients that used to have a greater impact in England. For instance doctors often added paracetamol to their routine prescriptions – pushing it up to the third most prescribed drug. (It is still in the top 10 in England).

"Prescriptions were cheaper so people would order large amounts of paracetamol to save money," Lehman says. This might explain why in Wales, where patients have not been charged for prescriptions since 2007, paracetamol is still the most prescribed drug.

Thyroid drugs

As life expectancy has increased, the medication doctors commonly prescribe has changed to cope with different long-term conditions – which could be one of the reasons for the dramatic increase in the popularity of thyroid drugs, says Dr McCabe. "There are a lot of thyroid problems around which, in part, might be a reflection of the ageing population," he says. But even so, Dr Joe Collier, emeritus professor of medicines policy at St George's University, is surprised to see levothyroxine so high on the list. "This is probably due to overdiagnosis of thyroid disease; it's likely to be a fad and possibly a dangerous one to boot, not least because it causes heart rhythm problems," he says. "I wonder if it is being prescribed to help some people lose weight."

The future

So what of the future? Will heart drugs remain at the top of the most prescribed lists in 20 years time? Chris Newton – managing director at BioFocus, an organisation of scientists working on new drug discovery – says that "research into heart and blood-pressure drugs is less prevalent today, partly because of previous successes in developing these drugs in the 80s and in managing these conditions in the early 90s. We are increasing our work on drugs for cancer, Alzheimer's disease, Parkinson's disease and Huntington's disease, because the genetic causes and biochemical processes of these conditions are much better understood now."

Top five drugs prescribed in England today

▶Simvastatin – for high cholesterol

▶Aspirin - for pain relief, angina, heart attack and stroke prevention ▶Levothyroxine Sodium – for underactive thyroid

▶Ramipril – for high blood pressure, heart failure, heart attack and stroke prevention

▶Bendro- flumethiazide – for high blood pressure and/or heart failure

Top five drugs prescribed in England 20 years ago

▶Salbutamol – for asthma or chronic obstructive pulmonary disease

▶Amoxicillin - antibiotic

▶Paracetamol - for pain relief

▶Co-proxamol - for pain relief

▶Beclomatasone - steroid inhaler for asthma