symptoms of nnn are similar to those of nicotine poisoning and include irritation at the point of absorption (for example, the gums when dipping tobacco is used), nausea and vomiting, sleep disturbances, headache, and chest pain. the substance is also a known carcinogen, meaning that any exposure to the substance can lead to cancer and is proven to cause esophageal and nasal cancer in animals. there is no known "safe" levels of nnn ingestion in humans due to its carcinogenic activity. however, in mice, the median lethal dose (ld) is 1g/kg.