See also nearby: Balfarg Riding School mortuary enclosure and henge
Within the 64.9 metres (213 ft) diameter henge were found broken Neolithic pottery, burnt wood and bone which had been dumped on the site prior to the erection of a 25 metres (82 ft) wide timber circle of 16 wooden posts. Two especially large portal timbers stood on the west side of the circle. It is likely that the henge was built after these phases of activity. Grooved ware pottery found in the postholes dates to around 2900 BC. Some of the vessels may have been used to hold black henbane (Hyoscyamus niger) which is a poison but also a powerful hallucinogen.
https://en.wikipedia.org/wiki/Balfarg
http://www.antiquity.ac.uk/ant/074/Ant0740049.htm
That link doesn't work for me, this one does https://www.cambridge.org/core/journals/antiquity/article/use-of-henbane-hyoscyamus-niger-l-as-a-hallucinogen-at-neolithic-ritual-sites-a-reevaluation/97178E89B2D5D0A582BDC0761AFABBCD The use of henbane (Hyoscyamus niger L.) as a hallucinogen at Neolithic ‘ritual’ sites: A re-evaluation. Antiquity, 74(283), 49-53.
However: It is difficult to use the evidence from Balfarg to support theories of the use of hallucinogens during the Neolithic. Such theories require substantial, reliable evidence from multiple sites where possible and, as such, the use of hallucinogenic drugs in prehistory cannot yet be conclusively demonstrated, using palaeobotanical evidence. This is not to say that hallucinogens were not used during the Scottish Neolithic: we need to keep looking for statistically reliable support. The debate must continue but not under the impression that scientifically reliable evidence is already there.
Something is not right. This message is just to keep things from messing up down the road