Chemists are trying to solve a scientific mystery involving marijuana brownies. Chocolate seems to throw off potency tests. That could be dangerous for consumers looking to relax, not hallucinate.

The finding is one example of chemistry's growing role in the marijuana industry. At the American Chemical Society meeting in San Diego this week, chemists will discuss the quirks of chocolate and other technical challenges surrounding marijuana-based products.

Marijuana contains hundreds of chemicals, including THC, which gets people high. David Dawson, a California chemist, tests marijuana chocolates for THC potency. He thinks some of the THC is clinging to the fat in chocolate, effectively hiding from the test.