In a surprising decision, the United States Food and Drug Administration has approved the weight loss drug called lorcaserin.
Lorcaserin is a type of medication called a "serotonin agonist" and this means that the manner in which it works bears some superficial similarity to the drug called fenfluramine which was the dangerous part of the "fen-phen" diet pill combination from the 1990s. Serotonin agonists are medications that work by binding DIRECTLY to proteins on cells called "serotonin receptors". What we have learned since the days of phen-fen is that there are actually several different types of serotonin receptors and that while fenfluramine would bind avidly to ALL of the receptor types, lorcaserin is engineered only to bind avidly to the serotonin receptors that are NOT associated with problems seen in phen-fen. In other words, lorcaserin is a more selective and very different type of serotonin agonist. On both these theoretical grounds and based upon the fact that pre-marketing clinical trials with lorcaserin failed to show any cardiac risk from lorcaserin, the FDA has made the decision for its approval.
In most studies with lorcaserin, it produces something like 5-7% loss of body weight (versus about 3% for placebo).
In order to understand Lorcaserin, we need to delve into a little organic and biochemistry. I'll try to keep the discussion fairly simple, but some of the details are crucially important.
Serotonin is a neurotransmitter (chemical 'messenger') that enables nerve cells (called 'neurons') to communicate with each other. Lorcaserin affects the brains's serotonin systems. In this regard only, Lorcaserin is like many safe and commonly prescribed anti-depressant medications called "selective serotonin re-uptake inhibitors" (SSRI's). There is however a serious and crucial difference between Lorcaserin and drugs like Prozac and Zoloft.
This means that the drug directly binds to and activates serotonin receptors. SSRI's like Prozac do not directly activate serotonin receptors. They are, as their name suggests, "reuptake inhibitors" that prolong the effect of naturally produced serotonin. Lorcaserin, on the other hand, does not affect reuptake of naturally produced serotonin. It instead mimics serotonin and directly binds to serotonin receptors and in so doing displaces, overpowers and prevents naturally occurring serotonin from affecting the same receptors.
Fenfluramine (whose brand name was Pondimin) was the "bad actor" in the infamous and disastrous fen-phen diet drug combination of the 1990s. Fenfluramine was a serotonin agonist that suppressed appetite. Unfortunately, it also caused cardiac fibrosis. This means that fenfluramine damaged the lining of the heart and also damaged the delicate valves of the heart. It did this because the lining of the heart (and its valves) called 'endocardium' contain receptors for serotonin that fenfluramine attached to and overpowered. This caused the cells of the endocardium to self-destruct and ultimately led to scarring and thickening of the entire lining of the heart.
Fenfluramine, Chlorphentermine, pergolide and cabergoline are all names for drugs that acted as serotonin agonists. All of these drugs were eventually withdrawn from the market because they were found to cause cardiac fibrosis.