Comparison of melatonin products against USP's nutritional supplements standards and other criteria

To evaluate and compare the quality of a sample of melatonin products, as measured by the United States Pharmacopeial Convention (USP) General Tests and Assays for Nutritional Supplements (other than Microbial Limits) and certain other tests.

Five immediate-release, two sublingual, and two controlled-release products were randomly gathered from a health food store, groceries, and pharmacies in the Baltimore-Washington metropolitan area.

Weight variation, disintegration (not applicable for controlled-release products), and drug dissolution, based on USP standards. Twelve-hour dissolution profiles were obtained from the controlled-release products. All tablets were also evaluated for friability following the USP procedure and for hardness following unofficial procedures.

All products passed the weight variation test. Two products showed excessive friability. Three immediate-release products failed both the disintegration and the dissolution tests. One of the three products demonstrated a threefold difference in hardness. One controlled-release product released 90% of melatonin in four hours in the dissolution test; the other released 90% of its content in 12 hours.

Some products showed evidence of poor formulation and/or poor quality control as indicated by excessive friability, failure to disintegrate and dissolve, and excessive variation in hardness. In vitro release profiles of the two controlled-release products were substantially different. The poor quality of some supplements should be a concern to consumers and health care providers.