Definition: "An ergogenic aid is any substance or phenomenon that enhances performance "

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Capromorelin: Pfizer's oral growth hormone booster

Pharmaceuticals companies are working on a new generation of oral substances that boost growth hormone production. One of these is capromorelin [structural formula shown below], which was developed by Pfizer. It works well enough to give 65+ subjects 2 kg extra of lean body mass in a year, which is not well enough for Pfizer to continue the research.

When combined with other substances, growth hormone is an effective doping substance. The disadvantage of growth hormone is that it is eliminated quickly from the body, and users have to inject it at least once and often several times a day, which is not a pleasant prospect.

But the body has receptors for proteins that stimulate the body to synthesise more growth hormone. If you're hungry, for example, your body produces the hunger hormone ghrelin. This hormone interacts with the GHS-1alpha receptor. If this receptor is stimulated the pituitary produces more growth hormone. Capromorelin looks different from ghrelin, but can also interact with the GHS-1alpha receptor.

The researchers tested capromorelin on 314 subjects aged over 65, and gave another 81 over 65s a placebo. After 2 months the researchers measured the subjects' IGF-1 concentration. Growth hormone stimulates the release of IGF-1 in the muscle cells and liver. It is via IGF-1 that growth hormone exerts its muscle-building effect and, handily, the concentration of IGF-1 is an indicator of the effectiveness of a GH booster.

10 mg tiw = 3 times 10 mg/week; 3 mg bid = 2 times 3 mg/day; 10 mg qhs = 10 mg/night; 10 mg bid = 2 times 10 mg/day.

Capromorelin: Pfizer's oral growth hormone booster

The most efficient dose is 2 times 3 mg/day. The figure above shows that the effect of capromorelin on the IGF-1 level remains constant throughout the period of a year.

Capromorelin: Pfizer's oral growth hormone booster

Capromorelin: Pfizer's oral growth hormone booster

Over a period of six months the subjects gained 1.4 kg lean body mass when they took 3 mg capromorelin twice a day. After a year the amount had risen to 2.5 kg lean body mass. The effects were not statistically significant, however. The test subjects did no physical exercise, so we don't know what capromorelin would do for bodybuilders.

The test subjects' condition did improve. The figure above shows how many feet [1 foot = 30.5 cm] extra they could cover in 6 minutes.

The researchers observed no serious side effects. The subjects did have more difficulty falling asleep and had bigger appetites, but despite this they did lose a small amount of fat.

The researchers published their study in 2009, when the project had already been stopped. The trial started in 1999 and was intended to last 2 years. The reason Pfizer gave up on capromorelin can be found in a review article published in 2008. [Clin Interv Aging. 2008; 3(1): 121-9.] "The study was unfortunately stopped, however, after all subjects had been treated for 6 and many for 12 months, due to failure to see an increase in per cent lean body mass, which was a pre-set non-efficacy termination criterion."

So it seems unlikely that we'll be hearing any more about capromorelin. Luckily for chemical athletes there are more oral GH boosters in the pipeline...

J Clin Endocrinol Metab. 2009 Apr;94(4):1198-206.

3N-GH lasts 24 times as long as regular growth hormone 07.12.2010