Who was dr. lanyon's letter for?

Dr. Lanyon's letter in "Strange Case of Dr Jekyll and Mr Hyde" was addressed to Dr. John Utterson. In the letter, Lanyon expresses his concerns about Dr. Jekyll's experiments and reveals his disapproval of Jekyll's scientific pursuits, which he deems unorthodox. The letter ultimately serves to convey Lanyon's shock and the disturbing events that transpired between Jekyll and Hyde.