"Ma Huang" is a Chinese shrub that has been used for centuries in traditional Chinese medicine as an anti-asthmatic and stimulant. This particular shrub contains not one, but TWO coumpounds that have 2 chiral centers - Ephedrine and Pseudoephedrine. Both these compounds are stereoisomers of 2-methylamino-1-phenyl-1propanol and are both optically active. The structural formula of 2-methylamino-1-phenylpropanol has two stereogenic carbons shown at Carbon #1 & #2. Each stereocenter can have an R or S configuration, so based on the general rule - a structure having n chiral centers will have 2^n possible combinations - there are 4 possible stereoisomers. In addition, these particular compounds exists as diastereomers to each other - Ephedrine is a diastereomer to pseudoephedrine.
In addition to the aforementioned uses, both ephedrine and pseudoephedrine can relieve hypotension - but pseudoephedrine has less effect. Other uses include weight loss promotion, nausea relief, and to treat bronchitis.