|One of these things is not like the other, one of these things can cause severe birth defects and lead to countless lawsuits|
So, what makes the drug so bad? It has to do with something called chirality. Certain chemicals with the same formula (in the case of Thalidomide, C13H10N2O4) are able to bind in slightly different ways. These forms can result in minor changes to how our bodies react to them, or can lead to some surprising differences. For example, another chiral molecule, limonene, smells like oranges in one form (the R enantiomer), and the other form (the S enantiomer) smells more like turpentine. Why is this? The proteins in our body have receptor sights that are very specific shapes. If one enantiomer fits, it's highly likely that the other one will not. Instead, it's common for the two forms to react with completely different proteins and lead to very different results.
|One defect resulting from Thalidomide|
Well, chiral molecules that occur in a racemic mixture (a mixture of both enantiomers) can be purified until only one enantiomer is present. So, why not do that? Then, it would treat morning sickness and not cause birth defects, right? Unfortunately, it's not that simple. Even when pure R-Thalidomide is given, the body freely converts the drug back and forth between the R and S forms. So, even if a patient is given only the beneficial enantiomer, some of the bad enantiomer will end up floating around in their blood stream. Even the good form is dangerous.
Interestingly enough, Thalidomide has not been completely taken off of the market. It is used to treat such diseases as leprosy, and is being researched as a treatment for cancer. It carries strong warnings about its potential for birth defects, but the side effects on the average, non-pregnant person are minimal. They are mainly limited to such things as dizziness and drowsiness.
Sources are the Thalomid Information, International Myeloma Foundation, PubMed Health, RxList, Drug Bank, Chinese University of Hong Kong, Ouvaton, Chirality & Odour Perception, MedicineNet, The New York Times, and Reuters. Images are from Wikimedia Commons under Creative Commons licenses or are copyright free: one, two.