Mechanism of Effect in Weight Loss
The effects of the ECA stack in weight loss are primarily due to the ephedrine component. Ephedrine acts both as a beta agonist and stimulates the release of noradrenaline. Increased circulating noradrenaline in the body then acts on white adipose tissue by increasing cAMP levels. This causes a thermogenic effect, raising body temperature by about 2 degrees and increasing the user's metabolism by 10% in conjunction with the rest of the stack.
However, the body's negative feedback system then activates to normalize the metabolism. This is done via the production of phosphodiesterase inside the cells, and prostaglandins outside the cell, which both lower cAMP levels within the cell.
Caffeine inhibits the production of phosphodiesterase inside the cell and therefore slows the cAMP breakdown. It also, by binding with and competitively inhibiting adenosine receptors in the brain, triggers the release of adrenaline which increases cAMP levels further.
Aspirin inhibits prostaglandin production outside of the cells, which, in conjunction with caffeine, greatly prolongs the thermogenic effects and increased metabolism by substaining elevated cAMP levels.
Ephedrine also has an anorectic, or appetite suppressant effect. The mechanisms behind this are not fully understood, but this aids in weight loss as well. However, these effects only last for about two weeks if the stack is not cycled as the body becomes tolerant to ephedrine to some degree. It is estimated that 60%–75% of the weight loss from using the ECA stack comes from the anorectic effect, and the remainder from thermogenesis.
The final component in weight loss of the ECA stack is that of a simple stimulant; the higher adrenaline and noradrenaline levels result in increased aerobic exercise performance and less fatigue.
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Mechanisms of Effect in Energy Gain
Ephedrine acts to increase energy by its actions as a sympathomimetic amine. It directly acts in the brain to increase the release of noradrenaline into the synapic cleft, and also partially serves as a noradrenaline reuptake inhibitor thereby also partially functioning as a dopamine reuptake inhibitor due to the shared action between the two terminals. Caffeine blocks adenosine receptors which lessens feelings of tiredness, and also increases dopamine levels, resulting in greater concentration, focus, and memory. The effects of caffeine on dopamine levels are usually short lived, but ephedrine's partial action as a dopamine reuptake inhibitor lengthens the duration.
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Dosage
Typically the ECA stack is consumed two or three times per day in a 1:10:10 or 1:10:15 ratio of ephedrine:caffeine:aspirin. These ratios vary across studies and across users but despite variance they all seem to be effective. Usually, no more than 25 mg of ephedrine, 200 mg of caffeine and 325 mg of asprin is consumed in a single dose. It is not recommended that the stack be taken past late afternoon as this may contribute to insomnia.
This is what I base my ECA stacks on.
Wikipedia's ECA Stack
