Methorphan

Methorphan comes in two forms
 * 1) Dextromethorphan - An over-the-counter cough suppressant
 * 2) Levomethorphan - The left hand isomer of the above, a potent acting opioid.

Racemethorphan
Racemethorphan is a racemic mixture of the stereoisomers of methorphan, namely dextromethorphan, which is the active ingredient in "DM" cough syrups, and the lesser known levomethorphan which is described as a controlled substance in The Merck Index - likely because it has more potential for abuse than its dextro enantiomer.

Levomethorphan is the methyl ether analog of levorphanol and these two substances are related in the same way that codeine (which is the methyl ether of morphine) is related to morphine.