A single pharmacogenetic test will tell me which drug will work for me

It's a myth!

Pharmacogenetics is a science designed to identify hereditary factors that affect your response to drugs. It is now known that certain genetic variations (specific characteristics of your DNA, what makes you unique) can determine how you react to a drug, whether in terms of how you will respond to treatment (optimally, sub-optimally or not at all) or in terms of the number and intensity of the side effects you will experience.

Since the sequencing of the human genome in 2003, knowledge of pharmacogenetics has advanced at an impressive rate! Unfortunately, the science of pharmacogenetics, which is based on probabilities, is not yet advanced enough to tell which drug will work for any given condition. This means that pharmacogenetic testing cannot predict 100% whether a drug will work or not, or whether it will cause side effects or not. However, pharmacogenetics can identify risk factors to help you make clinical decisions.

It should be noted that some new drugs now being prescribed require pharmacogenetic testing to ensure their effectiveness. This includes a drug called Ivacaftor, used to treat cystic fibrosis (a hereditary disease affecting certain glands in the lungs, liver, pancreas and intestines).