iso-LSD (more accurately named nor-iso-LSD or (+)-iso-LSD) is an inactive isomer of (+)-LSD, which is commonly synthesised alongside LSD in an partial or unsuccessful reaction, where the content ranges from 1% to 80% on average. It is thought to be the definition of 'bad acid', since it is widely thought to bind to the same receptors of LSD, hence diminishing it's action.
The other two isomers of LSD are (-)-LSD and (-)-iso-LSD and are also both inactive.
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