The ECA stack (Ephedrine, Caffeine, Aspirin) is a piece of bodybuilding woo. The idea is that taking ephedrine, caffeine, and aspirin every day will make your body burn more fat. It works insofar as ephedrine is speed, and that's about it.
The formula is typically a 1:10:10 or 1:10:15 ratio of ephedrine:caffeine:aspirin.
Excessive quantities of ephedrine cause heart attacks, so ECA stack supplements have now been banned. This has not, of course, stopped bodybuilders from using it for a moment.
 Supposed mechanism
Ephedrine is related to amphetamine. It ups your metabolism and suppresses your appetite. Caffeine raises your metabolism somewhat, pumps up your nervous system and makes you more likely to do things that use energy.
One claimed mechanism, found on an old Wikipedia article version, is:
- Ephedrine stimulates the release of norepinephrine, which preferentially burns white fat by increasing cAMP (cyclic adenosine monophosphate) levels.
- The body tries to renormalise cAMP levels within the cells via production of phosphodiesterase. So the l33t body hackers add caffeine to inhibit phosphodiesterase production.
- Aspirin inhibits prostaglandin production outside of the cells, which, in conjunction with caffeine, greatly prolongs the thermogenic effects and increased metabolism by sustaining elevated cAMP levels.
The individual pieces of this hypothetical body hack may (or may not) be accurate. The entire chain working out as described is suspiciously lacking in citable evidence. (If you ask proponents for evidence of the stack, they'll usually supply cut'n'pasted individual studies on each of the pieces perhaps doing something, but nothing supporting all of a claimed mechanism.)
Note also that this is only one claimed mechanism — if you look for the mechanism, you'll find a pile of explanations made of big words stuck together, all different. Mostly the idea is that ephedrine works like speed (though they don't phrase it like that), caffeine helps it along and aspirin helps them both along. Some suggest the aspirin is there in the hope of making the ephedrine less likely to make your heart explode.
The above claimed mechanism may become more popular (as a claim) — Tim Ferriss' magnum opus of broscience Four Hour Body claims the ECA stack is scientifically proven (though he advises against it as being unhealthy and dangerous), and when you look up the references, all he has is... the Wikipedia version the above came from. Sprinkled with "citation needed" and all.
 Science says ...
The E and C of the stack will cause weight loss — because, duh, it's speed — at about 1kg/month better than placebo, if you are already overweight-to-obese (so, not a bodybuilder) and eat properly and exercise. It does not, however, increase athletic performance. Science also seems to suggest these two parts of the stack taken separately (as in either using Ephedrine or Caffeine, but not both) is not very effective.
There are some unreplicated single studies suggesting caffeine plus ephedrine will increase athletic performance.
Caffeine causes secretion of adrenaline by the body which is good for slowing digestion (which suppresses appetite) and being awake and alert.
The aspirin part of the stack is just really a painkiller with little effect otherwise.
The stack does not preferentially target fat per se, the increase in metabolism and suppression of appetite (as with any speed) tends to cause the body to go after reserved energy (fat and muscle) more immediately. When the effects wear off, the body will go back to using what's in the digestive system. It does not enhance muscle-building per se at all. In the short term, it might allow you to work harder, however as with all stimulants, it also causes you to burn out much quicker. Long term health effects from too many stimulants include heart problems, urination problems, high blood sugar and a battery of psychosomatic effects.
The risks of ephedrine: heart attacks, strokes, difficulty sleeping, heavy perspiration (which can easily lead to dehydration), and talking shite at a mile a minute. Risks are increased during periods of physical exertion, heat and stress, e.g., working out.
The vendors tended to lie — a lot. The New England Journal of Medicine published a 2000 paper suggesting not very high risk, summarizing reports to the FDA up to 1999, and this paper seems to be a favorite of ECA stack advocates. But in 2002, Metabolife was compelled by the US Justice Department to turn over their adverse-event files — and had over 2,000 adverse event reports, ranging from insomnia to death, which they had withheld from the FDA and, by extension, the New England Journal of Medicine.
It's probably safer than crystal meth, though.
- ↑ According to Wikipedia. They'd know, after all.
- ↑ http://www.fda.gov/Safety/MedWatch/SafetyInformation/SafetyAlertsforHumanMedicalProducts/ucm152388.htm
- ↑ Unsourced mechanism chain on old version of the Wikipedia page, text removed for being completely spurious.
- ↑ "In total, these suggest that herbal ephedra/caffeine herbal supplements, when used as directed by healthy overweight men and women in combination with healthy diet and exercise habits, may be beneficial for weight reduction without significantly increased risk of adverse events." C N Boozer, P A Daly, P Home, J L Solomon, D Blanchard, J A Nasser, R Strauss and T Meredith "Herbal ephedra/caffeine for weight loss: a 6-month randomized safety and efficacy trial" Int J Obes May 2002, Volume 26, Number 5, Pages 593-604.
- ↑ https://www.ncbi.nlm.nih.gov/pubmed/8384187
- ↑ http://www.ncbi.nlm.nih.gov/pubmed/1619985
- ↑ "Evidence to support use of ephedra for athletic performance is insufficient." Paul G. Shekelle, MD, PhD; Mary L. Hardy, MD; Sally C. Morton, PhD; Margaret Maglione, MPP; Walter A. Mojica, MD, MPH; Marika J. Suttorp, MS; Shannon L. Rhodes, MFA; Lara Jungvig, BA; James Gagné, MD "Efficacy and Safety of Ephedra and Ephedrine for Weight Loss and Athletic Performance:A Meta-analysis" JAMA. 2003;289:1537-1545.
- ↑ http://www.ncbi.nlm.nih.gov/pubmed/1318281
- ↑ https://skeptics.stackexchange.com/questions/22/are-there-benefits-to-the-eca-stack-for-body-builders
- ↑ http://content.nejm.org/cgi/content/full/343/25/1833 — PMID 11117974
- ↑ http://oversight-archive.waxman.house.gov/documents/20040827102309-56026.pdf