Different medications are metabolized by different genes. I am not sure what gene metabolizes Carvedilol but I think it may be the same one which metabolizes a drug I had problems with – Metoprolol. As it turns out, even though everyone has the gene (CYP2D6), I had a particular variant which meant I did not effectively metabolize Metoprolol. The net result was that, instead of being absorbed and processed, it continued to circulate in my blood stream and could build up as more doses were taken. Thus the effects were multiplied. I had to be given a different drug which worked fine. This may not be your problem, but if you have not had a genetic test I would recommend one. I had my own testing done and had to convince my cardiologist and pharmacist that the drug was not appropriate for me. In fact, I am convinced that doctors and pharmacists should insist that genetic test be done to ensure that medicine can be tolerated by patients.