I have some experience of other drugs and testing, which may be useful to some people. Here are the facts that I know from experience:
Synthetic cannibinoids (spice) do not show up on a THC test.
Etizolam may show a positive on a dip test for benzodiazepines, but if tested by GC/MS will return a negative. This is because despite being in the same family as diazepam etc, etizolam is a thienodiazepine and has different metabolites which are not tested for in a laboratory test.
Nytol (diphenhydramine) does not trigger false positives for any drug on the multi panel tests I have used.
Here is a photo of a dip test for benzos, two days after taking Nytol and etizolam. A clear pass, meaning either both do not show up or they are cleared quickly from the system:
MDMA EXPERIMENT
I used half a gram of pure MDMA crystals on the Saturday night in question with last dose at around 5am on Sunday morning. Here are the results of my subsequent testing:
+55 hours:Ghost line
Unfortunately I ran out of testing strips but here is day +5, a strong pass. I would say that based on this evidence even quite heavy use of MDMA (half a gram in this instance) will clear in 3-4 days. However, be aware that it can apparently test positive for amphetamines and methamphetamine too, and I didn’t test for those this time.
Green Dragon Marijuana Detection Times 