you have to wait 30 days regardless. but lots of water, enough sleep. i've heard that a few bottles of grapefruit juice when you get out of a study helps get rid of whatever was in your system. this varies by med, and i express no medical opinion, it was just a thing i heard. don't go to a screening with grapefuit juice, milk thistle, any thing that looks like a masking agent, in your blood or urine. exercise when you get out of a study, lie around like a bum a few days before screening so your liver enzymes are settled down. for me it's essential to avoid coffee on the drive to a screening.
i recently wasted a trip out to vince. their study started more than 30 days after my last study, so i was going to screen for it, but it turns out they wanted a 30 day washout just to screen, which i had not understood. i don't know if that's common in the industry, or if it's always been that way at vince, or has to do with their new management. i'm a little rusty, i took a couple years off but am getting back into doing studies.
It's hard to tell what some of these places are aiming for. I was in a study and dosed with a food substance (that was the study) and told the recruiter, so I got to the screening and on vct they said "you can't be in a study until blahblah date because you were in a study". I told her what that was about and also that I disclosed all this info to the recruiter and she said it was ok to screen but I still got dq'd. I made them pay me the whole screening stipend because of travel. I think some sponsors do not want you to have any activity whatsoever for x amount of time, period. So if their protocol says "has not participated in the last 30 days" that includes screening day. I am suspicious that for the VCT system it doesn't let the sponsor pick "30 days from last dosing" or "30 days from last participation including follow-up" or "cannot screen for 30 days prior to last follow-up visit with another study" I think it just gives defaults like 30 day, 60 day, 90, etc. My disclosure said soing like the disqualification would be for "dosing with any study drug for 60 days prior" but I still got dq'd even though I was not dosing with a drug -- it was fructose! It's probably more about CYA than anything.