The name "phenethylamine" is not strictly correct, but fairly close. "Phen" is short for phenyl, the six-membered ring, "ethyl" refers to the two-carbon chain, and "amine" refers to the NH2, or nitrogen bonded to two hydrogens. An amine is more or less a nitrogen single-bonded to a carbon (there are some exceptions, but that's close enough for now).
Phenethylamine itself is a psychoactive drug all by itself, but some of its derivatives I imagine you've heard of before:
This is amphetamine, where we've basically stuck another carbon onto the carbon connected to the nitrogen. The squiggly line indicates a mixture of molecules where that carbon goes back into the screen and where it comes out of the page. The name is another truncation: alpha-methyl phenethylamine = amphetamine. This is one of the basic stimulants, sold under the brand name Adderall, Dexedrine, and others.
This is methamphetamine (or meth), where we've stuck a carbon onto amphetamine's nitrogen. Despite the media's fixation on meth as the latest drug-based moral panic, meth has been around since 1893 and used recreationally for more than 60 years. Though it is quite addictive and dangerous, it's worth noting that the majority by far of people who try meth do not go on to become addicts. For my money it's not all that different from regular amphetamine. Meth can be prescribed under the brand name Desoxyn for obesity and ADHD, though apparently it's also good for narcolepsy.
This is dopamine, another well-known neurotransmitter—a chemical that your brain uses to transmit signals. Here we've got hydroxyl (HO- = hydrogen connected to oxygen) groups stuck onto our six-membered ring. Once again, to pave over a lot of staggeringly complicated information, the similarity of phenethylamine-based drugs to this neural tool basically allows them to interact with the brain in a similar—but not identical—way and so temporarily alter brain function. This is not to say that they do the same things as dopamine, rather that they are close enough to dopamine's structure to get in and interact with the same places, with sometimes wildly varying effects.
This is methylenedioxymethamphetamine, or MDMA, better known to the world as ecstasy. You can see it's a cousin to meth with the oxygen-carbon-oxygen bridge on the left side, but the effects are markedly different. Subject to its own moral panic back in the 80's, it is not remotely as dangerous or addictive as meth. It does not eat holes in your brain. It will not instantly give you Parkinson's disease. Most of all, it does not kill 20% of the people that take it. In my opinion, from a psychological therapy basis, MDMA is probably the most promising chemical ever discovered. Fuck Prozac. Too bad the patent is expired so some drug company can't make $100 billion off this thing.
I've barely scraped the surface of the phenethylamines, but I'll be back at some point with part II. Part of why I love pharmacology is the sheer absurdity of it all. The idea that you can take ten or so carbons, a nitrogen, maybe an oxygen or two, and a few hydrogens, arrange them in the right way, take them, and the way you perceive and feel the world will change for a little while, is just weird. Subtract or add so much as a single carbon and the compound will change your perception in a completely different way, or not at all, or poison you. I find that utterly fascinating, gripping, in a way that strikes at the heart of some of the fundamental questions of life. If drugs aren't fascinating, I don't know what is.