Yesterday, the U.S. Food and Drug Administration approved the weight loss drug lorcaserin (Belviq^®, Arena Pharmaceuticals). This is the first approval for an obesity treatment since orlistat (Xenical^®) in 1999. The effect on weight loss is modest (3-5%) and the drug was studied versus placebo in combination with changes in diet and physical activity. Clearly not a miracle drug, but hopefully another useful tool in the management of this complex and extremely important issue.

At a glance, the most significant effect of the drug on patient management in rehabilitation appears to be an increase in hypoglycemia in patients with type 2 diabetes. Additionally, low back pain is listed as an adverse effect in the same population, though the mechanism for this is unclear. The drug appears to have its effect through activation of serotonin 2C receptors in the central nervous system. This means that other medications that activate serotonin receptors or increase serotonin levels may be problematic when taken in combination with lorcaserin, potentially producing a constellation of adverse effects known collectively as serotonin syndrome. Some antidepressants, drugs used to treat migraine headaches, and even herbal supplements such as St. John’s Wort and Panax ginseng are guilty as charged in this regard. Serotonin syndrome is characterized by

• cognitive signs & symptoms – headache, agitation, confusion, hallucinations
• autonomic signs & symptoms – hypertension, tachycardia, shivering, sweating, nausea, diarrhea
• neuromuscular signs & symptoms – tremor, myoclonus/twitching, hyperreflexia.

There is a case report in the physical therapy literature of a patient presenting with serotonin syndrome misdiagnosed as fibromyalgia. 

Neither the FDA nor Arena Pharmaceutical’s websites provided a date that the drug would be available for prescription. As with all new medications, we’ll have to wait and see how lorcaserin is used and what effects it has on individuals in the real world, outside of more carefully controlled clinical trials used to bring the drug to market. Come back and post in the comments if/when you see your patients taking it.