These are drugs which alter mood, behaviour, thought and perception in a manner similar to that seen in psychosis. Many natural products having hallucinogenic property have been discovered and used by man since prehistoric times.
HALLUCINOGENS
(Psychotomimetics, Psychedelics,
Psychodysleptics, Psychotogens)
These are drugs which
alter mood, behaviour, thought and perception in a manner similar to that seen
in psychosis. Many natural products having hallucinogenic property have been
discovered and used by man since prehistoric times. A number of synthetic
compounds have also been produced. The important ones are briefly described
below.
Lysergic Acid
Diethylamide (LSD)
Synthesized by Hofmann
(1938) who was working on chemistry of ergot alkaloids, and himself experienced
its hallucinogenic effect. It is the most potent psychedelic, 25–50 μg produces all the
effects. In addition to the mental effects, it produces pronounced central sympathetic
stimulation. Its action appears to involve serotonergic neuronal systems in
brain.
Lysergic Acid
Amide
A close relative of
LSD but 10 times less potent;
found in morning glory (Ipomoea violace) seeds.
Psilocybin
Found in a Mexican mushroom Psilocybe mexicana; it has been used by
Red Indian tribals during religious
rituals.
Harmine
It is present in a
vine Banisteriopsis
caapi, found in the Amazon region.
The Brazilian natives have used it as a snuff.
Bufotenin
Isolated from skin of
a toad (Bufo marinus). It is also found in
‘Cohaba Snuff’ and in the mushroom Amanita muscaria.
The above are all Indolealkylamines
related chemically to 5HT. A number of other synthetic derivatives like
Dimethyltryptamine (DMT) are also hallucinogenic.
Mescaline
From Mexican ‘Peyote
cactus’ Lophophora williamsi. It is a low potency
hallucinogen used by natives during
rituals. It is a phenylalkylamine but does not have marked sympathomimetic
effects.
Ecstasy
Methylene dioxy
methamphetamine (MDMA) is an amphetamine-like
synthetic compound with stimulant and hallucinogenic properties, that has been
abused as a recreational and euphoriant drug, especially by college students
under the name ‘Ecstasy’. Fear of
neurotoxicity has reduced its popularity.
Other synthetic phenylalkylamines with hallucinogenic property
are—Dimethoxymethyl amphetamine (DOM) and Methylene dioxyamphetamine (MDA).
High doses and repeated use of amphetamine can also cause psychosis.
Phencyclidine
It is an anticholinergic,
which activates receptors in brain causing disorientation, distortion of body
image, hallucinations and an anaesthetic like state: ketamine is a closely
related compound with lower hallucinogenic potential and is used in
anaesthesia.
Tetrahydrocannabinol
(9 THC)
It is the active principle of Cannabis indica (Marijuana). It has been the most popular
recreational and ritualistic intoxicant used for millennia. Its use has spread
world wide. The following are the various forms in which it is used.
Bhang the dried leaves—is generally taken by oral route, acts slowly.
Ganja the dried female inflorescence—is more potent and is smoked: effects are produced
almost instantaneously.
Charas is the dried resinous extract from the flowering tops and leaves—most potent, smoked
with tobacco; also called ‘hashish’.
Cannabis is the drug of abuse having lowest acute toxicity.
Considerable insight
has been obtained recently in cannabinoid pharmacology. Since 1990 two cannabinoid receptors CB1 (in CNS) and CB2 (in peripheral tissues) have been identified and cloned. A host
of endogenous ligands for the cannabinoid receptors have also been isolated. Anandamide the ethanolamide of
arachidonic acid is the principal endocannabinoid synthesized in the brain.
Endocannabinoids are released by macrophages during haemorrhagic shock and
cause fall in BP. However, all actions of cannabis are not mimicked by anandamide.
Cannabis produces
potent analgesic, antiemetic, anti-inflammatory and many other pharmacological
actions. The crude herb, its active constituents and some synthetic analogues
have been tried in a variety of conditions and many potential clinical applications
are proposed.
ü To ameliorate muscle
spasm and pain in multiple sclerosis, and certain dystonias.
ü Cancer chemotherapy
induced vomiting: the synthetic cannabinoids nabilone and dronabinol are
licenced for this use.
ü As a neuronal
protective after head injury and cerebral ischaemia.
ü To relieve anxiety;
migraine.
ü To reduce i.o.t. in
glaucoma.
ü As appetite stimulant.
ü As bronchodilator in
asthma.
However, the
hallucinogenic and psychomotor effects are a limitation; non-hallucinogenic
congeners are being investigated.
The hallucinogens, in
general, produce a dreamlike state with disorientation, loss of contact with
reality, field of vision may appear to sway and objects distorted like images
in a curved mirror, faces may appear grotesque. On closing the eyes an unending
series of colourful, very realistic and fantastic images appear to surge; time
sense is altered, music appears tangible. Ability to concentrate is impaired,
one can read but does not know what he is reading; however, ataxia is not prominent.
Many feel relaxed and supremely happy, may laugh uncontrollably or may become
sad and weep. With higher doses—panic reactions and sinking sensation are
common.
Some degree of
tolerance occurs, but reverse tolerance is not unusual.
Psychological
dependence on hallucinogens may be mild (occasional trips) to marked
(compulsive abuse), but physical dependence does not occur. All are drugs of
abuse.
Hallucinogens have
been rarely used in psychiatry to facilitate conversation and for opening up
the inner self in case of withdrawn patients.
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