The cinnamoyl-CoA is then reacted with a hydratase to attach the alcohol functional group. The product is then reacted with a retro-aldolase, forming benzaldehyde. Benzaldehyde reacts with pyruvic acid to attach a 2 carbon unit. This product then undergoes transamination and methylation to form ephedrine and its stereoisomer, pseudoephedrine. Mechanism of action
Ephedrine, a sympathomimetic amine, acts on part of the sympathetic nervous system (SNS). The principal mechanism of action relies on its indirect stimulation of the adrenergic receptor system by increasing the activity of norepinephrine at the postsynaptic α  and β receptors. The presence of direct interactions with α receptors is unlikely, but still controversial. L-ephedrine, and particularly its stereoisomer norpseudoephedrine (which is also present in Catha edulis) has indirect sympathomimetic effects and due to its ability to cross the blood-brain barrier, it is a CNS stimulant similar to amphetamines, but less pronounced, as it releases noradrenaline and dopamine in the substantia nigra.The presence of an N-methyl group decreases binding affinities at α receptors, compared with norephedrine. Ephedrine, though, binds better than N-methylephedrine, which has an additional methyl group at the nitrogen atom. Also the steric orientation of the hydroxyl group is important for receptor binding and functional activity. Compounds with decreasing α-receptor affinity

History
Asia
Ephedrine in its natural form, known as máhuáng (麻黄) in traditional Chinese medicine, has been documented in China since the Han dynasty (206 BC – 220 AD) as an antiasthmatic and stimulant.
Medical use
Both ephedrine and pseudoephedrine increase blood pressure and act as bronchodilators, with pseudoephedrine having considerably less effect.Ephedrine may decrease motion sickness, but it has mainly been used to decrease the sedating effects of other medications used for motion sickness.Ephedrine is also found to have quick and long-lasting responsiveness in congenital myasthenic syndrome in early childhood and also even in the adults with a novel COLQ mutation. Weight loss
Ephedrine promotes modest short-term weight loss, specifically fat loss, but its long-term effects are unknown. In mice, ephedrine is known to stimulate thermogenesis in the brown adipose tissue, but because adult humans have only small amounts of brown fat, thermogenesis is assumed  to take place mostly in the skeletal muscle. Ephedrine also decreases gastric emptying. Methylxanthines such as caffeine and theophylline have a synergistic effect with ephedrine with respect to weight loss. This led to creation and marketing of compound products. One of them, known as the ECA stack, contains ephedrine with caffeine and aspirin. It is a popular supplement taken by bodybuilders seeking to cut body fat before a competition. Recreational use
As a phenethylamine, ephedrine has a similar chemical structure to amphetamines and is a methamphetamine analogue having the methamphetamine structure with a hydroxyl group at the β position. Because of ephedrines structural similarity to methamphetamine, it can be used to create methamphetamine using chemical reduction in which ephedrines hydroxyl group is removed; this has made ephedrine a highly sought-after chemical precursor in the illicit manufacture of methamphetamine.