The proof I was referring to is in the forms of clinicalscientific studies that doctorsscientists in the article refer to when explaining the nature of drugs in the bodyThe doctors contacted by The Chronicle agreed that drug residue can remain in fat for a short time but not indefinitely The longest we know that THC the active substance in marijuana stays in the fat is about a month For ecstasy and LSD were talking about a day or two said Dr Neal Benowitz  head of clinical pharmacology at UCSF