Could this be the reason your pills are not working? From headaches to hayfever, how the effectiveness of drugs can vary from person to person By Lucy Elkins Why is it that while a friend swears by a certain type of painkiller, you find it does nothing for you? Scientists are discovering that people react to medications differently - and what may work for some might have no effect for others. It's often down to a variation in our genes, explains Jayne Lawrence, professor of biophysical pharmaceutics at the Royal Pharmaceutical Society. Your genes affect how your body breaks down and transports a drug. Here, Lucy Elkins looks at the drugs where the effectiveness varies massively from person to person. Hayfever: Sometimes the levels of the allergen are so overwhelming that antihistamines alone are not enough Antihistamines are the usual first-line treatment for allergies. They work by suppressing the action of histamine, a chemical produced by the body that leads to allergic symptoms such as itching and wheezing. Sometimes, though, the levels of the allergen are so overwhelming that antihistamines alone are not enough. In this case, monteleukast can be prescribed. This works by stopping part of the process that leads to the release of histamine. Montelukast will not work for one-third of patients. "There appears to be a genetic reason," says Dr Adam Frosh, a consultant ear, nose and throat specialist at the East and North Hertfordshire NHS Trust. A small study at Frimley Park Hospital, Surrey, published this year found montelukast helped reduce the symptoms of urticaria - red, itchy rash triggered by allergy - in 12 people. However, it had no effect in 11 others and in two people made symptoms worse. WHAT TO TRY INSTEAD: Steroid sprays are often an effective treatment for a runny, irritated nose linked to an allergy (such as hayfever). Allergies can be treated with more specialised forms of therapy such as desensitisation, where tiny amounts of the allergen are injected into the body over time, until the body has built up a tolerance to it. Codeine is a popular painkiller and is found in over-the-counter pain relief such as Panadol Ultra or Solpadeine. It is one of the opiod drugs (which also includes morphine) and works by helping block pain signals from the nerves to the brain, thus reducing discomfort. It is used for short-term moderate pain such as dental pain. Around 15 per cent of people get no benefit from this drug. This is because they have a genetic variation to an enzyme called cytochrome P450 2C9. "Codeine needs to be metabolised by the body into morphine to provide pain relief, but people with this genetic variation do not have this enzyme," says Professor Lawrence. This means they get little or no pain relief from this. WHAT TO TRY INSTEAD: Paracetamol or ibuprofen will work. If pain is more severe, opiate-based painkillers such as morphine may be prescribed. The triptan drugs were hailed as a great hope for migraine sufferers when they were introduced in the Nineties. If taken when symptoms start, they may halt a migraine in its tracks. Triptans are thought to work by raising levels of the naturally occurring chemical serotonin. Migraines: For 30 to 40 per cent of people, triptans do not reduce the symptoms of the migraine This, in turn, may lower the number of pain signals being sent from the trigeminal nerve, one of the head's major nerves. Serotonin also helps ease other symptoms, such as nausea and visual disturbances. There are seven different types of triptans, which are available as a tablet, nasal spray or injection. Some are available over the counter, but stronger doses are prescription only. Studies have found that in around 30 to 40 per cent of people, triptans do not reduce the symptoms of the migraine. "We don't know for sure why this is," says Dr Andrew Dowson, director of headache services at King's College Hospital in London. One theory is that the effect of serotonin on migraine varies from person to person, so although triptans will reduce symptoms in some, in others they will have no effect. WHAT TO TRY INSTEAD: "Sometimes we find that giving a non-steroidal anti-inflammatory painkiller such as ibuprofen at the same time as the triptan improves the chance of success," says Dr Dowson. They can also be combined with other drugs that aid gastric emptying, such as domperidone. This is because many treatments need to be absorbed through the stomach to work properly. However, for some reason, migraines can slow the movement of food and liquid through the stomach, delaying drug absorption. If a gastric drug fails then another option is to treat each symptom individually - for example, by giving cinnarizine to reduce dizziness or an anti-sickness drug such as prochlorperazine to prevent nausea. If left untreated, high blood pressure can lead to strokes and heart attacks. There are many different types of medication used to counter the condition, because there is no single pill that fits all. Blood pressure: Age, weight and ethnicity influence the effectiveness of tablets If your blood pressure is not under control, it could be that you need different medication. "Age, being overweight and ethnicity influence the effectiveness of blood-pressure pills," says Neil Poulter, professor of preventive cardiovascular medicine at the National Heart and Lung Institute, Imperial College London. This is largely due to the hormone renin, which constricts blood vessels, contributing to high blood pressure. Some of the commonly used blood pressure medications - ACE inhibitors or angiotensin-receptor blockers (ARBs) - work by preventing renin from constricting blood vessels. However, if you already have low levels of this hormone, then other factors may be causing your high blood pressure. Older people and those of African descent tend to have lower levels of this hormone, so the standard drugs will not work so well. WHAT TO TRY INSTEAD: Patients will most likely be prescribed calcium channel blockers such as amlodipine. Calcium narrows blood vessels, increasing blood pressure - these drugs block the action of calcium, helping to relax the vessels and lower pressure. If these do not work, then diuretics may also be prescribed, which help reduce the amount of fluid in the bloodstream, reducing pressure. Antidepressants are designed to increase levels of feel-good chemicals in the brain. There are around 47 million NHS prescriptions issued for antidepressants every year. Around half of all those who try antidepressants find they don't work. A study published in the Journal of the American Medical Association in 2010 concluded that antidepressants are little better than a sugar pill for treating mild depression. The researchers said the more severe the depression, the better the effects. WHAT TO TRY INSTEAD: Talking therapies, such as cognitive behavioural therapy, which try to change the way a person looks at the world, may help. "The other important thing to do is to avoid loneliness and keep busy," says Dr Paul Blenkiron, consultant psychiatrist at NHS Bootham Park Hospital, York. Exercise both body and mind. Try to get physical exercise two or three times a week - even a stroll will help.