I continue to be impressed with the notion of precision medicine. The science is actually in its infancy. One of the things that I now feel a bit embarrassed about is the conversations I have had with patients about side effects they felt that they were having with medications that I prescribed. This includes antibiotics, cough medications, and even varieties of bronchodilators. Most of the time I was very skeptical about what I was being told but, more recently, I have tried to be more understanding. Unfortunately, most insurance companies have formularies which do not allow for many variations on medications.
Let me give you one specific example of how your own personal genetic code can influence the medications you take. Codeine is metabolized to morphine when you take it, but there are at least 100 genetic variants to the enzyme that does this. Some will cause the codeine to be metabolized slowly, and others more quickly. This can lead to important consequences, some of which can be life threatening. Codeine, when given to children that are ultra rapid metabolizers, has resulted in death in several instances. The same can happen to adults. It is one of the reasons that I have been very reluctant recently to prescribe codeine to my patients.
Of course not every symptom is related to a medication issue, but I am surprised that many of my patients, who take a long list of medications, do not have more problems. Fortunately, the effect of genetics is usually rare.