Leucine - This essential amino acid, branch-chained like valine and isoleucine, makes up about a third of muscle protein. So besides serving as a secretogogue, studies have shown leucine to minimize the loss of muscle mass in patients recovering from surgery or severe trauma.

Glycine - While glycine also serves as a secretogogue, it is most commonly used in conjunction with arginine and ornithine in raising HGH levels.

Valine - This is another branched-chain amino acid abundant in muscle tissue. It is a necessary substrate for two other amino acids, glutamine and alanine, which are released in large quantities during intense exercise. Since, like other branched-chain secretogogues, valine is used up by the muscles, it spares other amino acids from being catabolized. Besides having shown itself to be an HGH releaser, it also promotes increased muscle mass and strength, which in turn also helps to offset the aging process.

Carnitine - In addition to functioning as a secretogogue, carnitine also helps promote weight loss. It does this by assisting in transporting long fatty acid chains to muscle tissue, where it can be metabolized.

Tryptophan - This amino acid is a neurotransmitter precursor. It induces a calming effect, so is effective in treating anxiety and stress. Besides acting directly to induce HGH release from the pituitary, it also assists in this by means of its secondary effect of countering insomnia. Since one of the largest pulses of HGH release from the pituitary occurs in early sleep, by acting as a soporific, tryptophan conduces to this end by effecting this valuable early sleep.

Tyrosine - Tyrosine is a biochemical precursor to the neurotransmitter, dopamine. As such it affects HGH levels indirectly. That is, if a reserve of tyrosine is available, dopamine levels can be kept higher; and dopamine, amongst other things, acts as an HGH releaser. Tyrosine also produces a stimulating effect and blocks the calming and soporific effects of tryptophan. It also improves nerve transmission from the brain to the muscles, stimulating more motor units and conferring higher strength levels. There is some attenuation of its effects and therefore it should not be used on a regular, ongoing basis.

Gamma Amino Butyric Acid (GABA) - GABA acts as an effective HGH releaser and confers a pleasant, relaxing, calming effect, somewhat in the manner of tryptophan.