Experts suspect that dextromethorphan (DXM) may be the main active ingredient in so-called 'Snurf' pills, sold online and blamed for sickening four Pennsylvania teenagers this week, WebMD reported Sept. 9.

DXM is the main ingredient in cough medications like Robitussin and other over-the-counter products, which themselves have grown in popularity as drugs of abuse, especially among younger teens.

The ingredients in the Snurf pills remain a mystery: the packaging claims they are herbal and include "fevizia, palenzia, and de la Amazon," but no such herbs exist. Other products, sold as Snuffadelic and Red Dawn Vector Euphoria Enhancer, claim to have the same ingredients.

The drugs are not illegal, but experts warn that the "herbal" label may fool teens into thinking that they are safe.