Jet black tongue is seen with toxicity of:

Usual symptoms of cocaine poisoning are anorexia, pale face, sunken eyes, insomnia, digestive disturbances, impotence, Defective memory, physical and mental degeneration, mydriasis, tachycardia hypeension and tachypnoea. Mental changes include hallucination, delusion of persecution, depression and derangement of special senses. Tactile hallucinations are common. Feeling of crawling of insects on skin as sand bags lying under the skin are repoed (cocaine bugs).The teeth and tongue appear jet black in cocaine poisoning. Ref: Concise Textbook of Forensic Medicine & Toxicology By R.K Sharma; 2/e, Page 303