Natural production of human growth hormone peaks in puberty, transforming fat into muscle and causing youngsters to sprout up. A synthetic version of the hormone is used to treat deficiencies, which can result in slowed growth or even dwarfism. (The drug has for that reason become something of a designer drug for tiger moms who fear for their child’s height.)

For athletic doping hGH is used for its muscle-building effects. As of the 2012 Olympics a new drug test should be better able to detect hGH doping than ever before. Previous testing relied on “isoform” ratios: Natural hGH comes in two different weights, or isoforms, but synthetic hGH comes in only one weight. Therefore if an athlete has injected synthetic hGH the ratio of weights will be tilted to one side. The problem is that the body corrects the ratio within a day or two. 

The new test instead looks for hGH’s knock-on effects in the body – namely, increased production of insulin-like growth factor 1 (IGF-1) and a substance called P3NP. That extends detection to at least a week after doping.