http://en.wikipedia.org/wiki/Concrete
scroll down to find your answer, or refer to the contents list, don't be lazy like me, can't even be bothered to hyperlink it.
i also wonder if long term medication can have side effects on you. fined if you have medical condition evaualted by specialist in details and know you have to take medication everyday to subdue keep it under control then no choice. if no sure of root cause yet better approach medication with caution.
last time my firend the hour before medical checkup go shoot chicken. then immediately go for urine test (he never urinate and clear the chunk still present in his didi) doc check urine say got protein in his urine write a letter to refer him to specialist. lucky he never go, another doc earning money trick.
then my friedn case is like that when he drink sweet beverages his urine will be yellow in color. when he drink plain water and drink in excess until he will have the feeling of visiting the toilet often his urine color will be clear. you do this variation before medical urine test you see the results will be differnt. so how accurate is the medical report? SOme cases really is no speciic instructions given to patients before goinf fot chekup to have accurate readings taken. of course x-ray on bones, chest etc, height and vision usually are constant. weight blood pressure varies really. my friend also told me his blood pressure although on the high side in the past can pass medical checkup if he relax and don't remain in a cold acon room for prolonged period of time. now his medical checkup doc psycho him to use mediince so that the reading can go down and the test can pass. one tablet costs sgd$1.30++. although my friend got savings but he never use it cost he need it to service his flat in the event he get jobless again, shit can it on ffloor traps, but this is not the way money to spend. silly classic toaist buddhist christianity mindset. now he taking the medicine trial one day first to see if have any drosiness effects or not. if not under probabtion how to work properly. may cause drowsiness also never declare on the medicine package. if so just instruct to take dosage by evening lah!