There are many drugs in the market, both legal and illegal and also some others which do not even have a classification, usually some new substance which is still to be investigated by the authorities. All of these drugs have various qualities and effects on the human body, but some are very well known to cause hallucinations and are usually called hallucinogenic drugs.
Among these the most famous ones are:
LSD (i.e. lysergic acid diethylamide and also known as just “acid”)
Psilocybin (much more famous by their colloquial name – “mushrooms”)
Ecstasy (also known as MDMA)
Mescaline (or known also as “peyote”)
Hallucinations timing is important
When we talk about hypnagogic hallucinations (and also hypnopompic) then we are speaking about hallucinations which occur specifically right before falling asleep and right before waking up and this means that other types of hallucinations, for example during the day, are not classified as part of these. So if someone is taking various drugs or chemicals and experiencing hallucinations then these are not necessarily hypnagogic hallucinations.
That said, drugs and chemicals do have effects which last a varied amount of time depending on each specific drug. This means that these substances which people are using take time for the body to absorb and get rid of and some of the substances can be destroyed by the body faster and others are more difficult. Therefore a healthy person could be suffering from sleep disorders like hypnagogic hallucinations as a consequence of taking these drugs because the body is not at its healthy state and is being influenced or “attacked by” various chemicals.
Withdrawal from drugs
Finally if someone has decided to change their life for the better and is working to stop taking drugs they will have to pass through the withdrawal period where the addiction is being destroyed and the body is re-adjusting internally back to its healthy state. While in this period the body is not behaving in a normal way and hypnagogic hallucinations can be experienced in this phrase also.