This page lists commonly available deliriant antidotes.
Physostigmine is a compound known to reverse the effects of anticholinergics such as datura and DPH. As an inhibitor of the enzyme which breaks down acetylcholine, physostigmine counteracts the effects of deliriants on the central nervous system and peripheral nervous system. As physostigmine is a prescription-only drug in most locations, it cannot often be reliably obtained. Physostigmine is used to reverse deliriant poisoning in hospitals.
Nicotine is often cited as a potential trip-reducer to have nearby during a deliriant experience. Nicotine counteracts some of the effects deliriants produce on memory and cognition via activation of the nicotinic acetylcholine receptor. Despite this, the efficacy of nicotine in this application is disputed, and many people report that nicotine does not work as a deliriant antidote at all. While nicotine is often effective in reducing some of the more uncomfortable effects of deliriants and can be kept on hand if one desires, it should not be trusted as a reliable antidote, especially if one regularly uses it.
It should also be noted that nicotine is regarded as a highly addictive compound. Harm reduction should always be practiced if one decides to use nicotine.