Some drug molecules are chiral, and the enantiomers have different effects on biological entities. They can be sold as one enantiomer or as a racemic mixture. Examples include thalidomide, ibuprofen, cetirizine and salbutamol. A well known drug that has different effects depending on its ratio of enantiomers is amphetamine. Adderall is an unequal mixture of both amphetamine enantiomers. A single Adderall dose combines the neutral sulfate salts of dextroamphetamine and amphetamine, with the dextro isomer of amphetamine saccharate and D/L-amphetamine aspartate monohydrate. The original Benzedrine was a racemic mixture, and isolated dextroamphetamine was later introduced to the market as Dexedrine. The prescription analgesic tramadol is also a racemate.
In some cases (e.g., ibuprofen and thalidomide), the enantiomers interconvert or racemize in vivo. This means that preparing a pure enantiomer for medication is largely pointless. However, sometimes samples containing pure enantiomers may be made and sold at a higher cost in cases where the use requires specifically one isomer (e.g., for a stereospecific reagent); compare omeprazole and esomeprazole. Moving from a racemic drug to a chiral specific drug may be done for a better safety profile or an improved therapeutic index. This process is called chiral switching and the resulting enantiopure drug is called a chiral switch. As examples, esomeprazole is a chiral switch of  (±)-omeprazole and levocetirizine is a chiral switch of (±)-cetirizine.
While often only one enantiomer of the drug may be active, there are cases in which the other enantiomer is harmful, like salbutamol and thalidomide. The (R) enantiomer of thalidomide is effective against morning sickness, while the (S) enantiomer is teratogenic, causing birth defects. Since the drug racemizes, the drug cannot be considered safe for use by women of child-bearing age, and its use is tightly controlled when used for treating other illness.
Methamphetamine is available by prescription under the brand name Desoxyn. The active component of Desoxyn is dextromethamphetamine hydrochloride. This is the right-handed isomer of methamphetamine. The left-handed isomer of methamphetamine, levomethamphetamine, is an OTC drug that is less centrally-acting and more peripherally-acting. Methedrine during the 20th century was a 50:50 racemic mixture of both methamphetamine isomers (levo and dextro).