In terms of molecular structure, synephrine has a phenethylamine skeleton, with a phenolic hydroxy - group, an alcoholic hydroxy- group, and an N -methylated amino -group. Alternatively, synephrine might be described as a phenylethanolamine with an N -methyl and p -hydroxy substituent. The amino-group confers basic properties on the molecule, whereas the phenolic –OH group is weakly acidic: the apparent (see original article for discussion) pK a s for protonated synephrine are (phenolic H) and (ammonium H). 
Okay, who wrote this: "its use in methamphetamine manufacture"? Regardless, I removed it as any chemist can see that it's very difficult to bring about such a transformation as one would need to destroy the ethylamine backbone in order to make the isopropylamine, and that's to say nothing about the aromatic hydroxyl. Methamphetamine is impossible (on a practical level) to make from phenylephrine and the chemistry of the latter is sufficiently similar with that of the title compound to have made the above statement stand out in the mind of most lay people (yes, even non-chemists). —Preceding unsigned comment added by ( talk ) 03:48, 19 May 2009 (UTC)
Pseudoephedrine and phenylephrine are both used as decongestants; and, until recently, pseudoephedrine was much more commonly available in the United States. This has changed because provisions of the Combat Methamphetamine Epidemic Act of 2005 placed restrictions on the sale of pseudoephedrine products to prevent the clandestine manufacture of methamphetamine . Since 2004, phenylephrine has been increasingly marketed as a substitute for pseudoephedrine; some manufacturers have changed the active ingredients of products to avoid the restrictions on sales.  Phenylephrine has been off patent for some time, and many generic brands are available.