Biochemically, falling in love is pretty much like getting simultaneously smashed on low-dose speed, E, and heroin. That's because most of the recreational substances we indulge in, work on exactly the same brain bits that love does. It all comes down to what love does to a couple of chemicals in your brain: dopamine and noradrenaline.
Dopamine and noradrenaline are neurotransmitters - they get released from nerve cells, switch on other nerve cells that are sensitive to them, and then get reabsorbed. (Complicate that by a factor of about 40 zillion and you're somewhere near the reality of how the brain works, because by switching on nerve cells in the brain, these chemicals control everything from hormone release to mood, anxiety and blood pressure).
Somehow, through all of its actions, dopamine regulates our mood. At the extremes, it's responsible for Parkinson's disease (not enough dopamine) and the symptoms of schizophrenia (a tad too much), but generally it just makes us feel good. Noradrenaline works by triggering the release of adrenaline, the hormone that gets us ready to fight or run. As well as the always delightful heart palpitations, blushing, and butterflies, noradrenaline gives us the drive to enjoy life.
When it comes to love, we each produce our own hit of speed to get things going - phenylethylamine (PEA), a kind of amphetamine that releases a flood of dopamine and noradrenaline and all that goes with them. As well as in the minds of the love sick, PEA is found in chocolates, but in levels so small they probably don't explain our addiction to the stuff. It's also a close relative of methylenedioxymethamphetamine - thankfully shortened to both MDMA and ecstasy. The big biological drawback with ecstasy is that it kills parts of some nerve cells - making them swell and burst. Nasty stuff.
As well as PEA, lovin' action gives us a hit of our very own version of heroin - endorphins. These babies have the same pain-killing,