How many letters does the top answer for “any substance that can cause a rise in body temperature” have?

The most common answer is pyrectic (8 letters).

Crossword clue: any substance that can cause a rise in body temperature

2 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

pyrectic 8 letters wn-def

any substance that can cause a rise in body temperature

pyrogen 7 letters wn-def

any substance that can cause a rise in body temperature

any substance that can cause an allergy 50% similar → allergen