The authority said DNP (2,4-dinitrophenol) continued to be sold and consumed in capsule and powder form.
"This can and does kill. That’s why we are urgently warning the public not to take any tablets, capsules, powders or liquids containing this deadly ingredient. DNP is an industrial chemical that is not fit for human consumption," it said in an announcement.
It urged the public to help it "spread the word to prevent another death" with the social media hashtag #DNPkills.
The campaign follows the death of Eloise Aimee Parry, a university student from Shrewsbury, who died after taking eight tablets that contained DNP last month. She was said to have bought the product online. The 21 year old was the latest of several fatalities related the substance over the last few years.
Its youngest known British victim was 18 years old.
DNP is used by those looking to lose weight as well as the body building community.
DNP is also known as:
It burns fat by speeding up metabolism to a dangerously high level and at best induces nausea, vomiting, restlessness, flushed skin, sweating, dizziness, headaches, rapid respiration and irregular heartbeat. At worse it can put the user into a coma or lead to death.
The FSA said consuming lower amounts over a long period of time could lead to cataracts and skin lesions and affect the heart and nervous system.
The substance is banned or has been officially warned about in many countries including the UK.
The FSA will be tweeting to raise awareness from its @foodgov account in late April and early May. The warning tweets focus on DNP's weight loss and body building uses, asking: "Are you dying to be thinner?" and "Killing yourself to be bigger?"
The campaign is supported by UK eating disorder charity Beat.