The stock price of Pfizer Inc. (NYSE: PFE) has been declining this morning. Pfizer canceled the development of an obesity drug for which many had high hopes, especially in light of the looming 2011 Lipitor blockbuster cholesterol drug patent expiration. Pfizer may find it hard to post growth without it.

Pfizer is not the only pharma that has recently canceled the same class of obesity drugs. Only Wednesday, Sanofy Aventis (NYSE: SNY), after stopping sales in Europe of its version of the drug, Acomplia, also stopped clinical trials on humans. Merck & Co. (NYSE: MRK) stopped development of a similar drug candidate called Taranabant a few weeks ago. Those companies all had high hopes the drug could be used for smoking, diabetes and high cholesterol along with obesity. According to Bloomberg, only Bristol-Myers Squibb Co. (NYSE: BMY) is still developing a similar medicine.

Why are they all stopping? Mostly because they figured regulators around the world will not approve the drug due to negative psychiatric side-effects. This class of drug works on blocking the pleasure centers in the brain, specifically, it blocks the cannabinoid type 1, or CB1, receptors. If cannabinoid sounds familiar, it is because this is the very same pleasure centers that give marijuana smokers the "munchies." By blocking these centers, studies have shown people have become depressed and had suicidal thoughts.

Perhaps not having chemical and pharmaceutical degrees I'm missing something, but it seems rather straight forward that if one's pleasure centers are blocked, depression could ensue. Even if it just blocks one specific type, that could be enough to create an imbalance.

Usually regulators weigh costs, risks and benefits of the drug and the condition treated, often approving drugs with severe side effects. These drugs are our best option currently. But drug companies should change their attitude somewhat, and when developing new drugs, place more emphasis on looking at the the body as one whole entity, and see how the drug interacts with the rest of the body, not just if it can treat the specific condition.