Pediatric emergency medicine trisk 3147 3147
Bạn đang xem bản rút gọn của tài liệu. Xem và tải ngay bản đầy đủ của tài liệu tại đây (99.7 KB, 1 trang )
When smoked or vaporized, THC is absorbed via the lungs. It is estimated that
no more than 50% of the THC inhaled in a marijuana cigarette is actually
absorbed. Pharmacologic effects begin immediately. In contrast, the onset of
effects after oral ingestion occurs in 30 minutes to 1 hour, and peak effects may
not occur until the second and third hours after ingestion. Oral ingestion of
cannabis typically results in decreased bioavailability because of hepatic firstpass metabolism but more prolonged effects because of ongoing slow absorption
via the GI tract. The difference in kinetics of smoked versus oral cannabis has led
to edible THC overdoses in users who ingest multiple doses before the first dose
has begun to take effect.
THC readily crosses the blood–brain barrier and binds to endogenous
cannabinoid receptors in the CNS and periphery.
Clinical Considerations
The most prominent effects in humans are on the CNS and cardiovascular system.
In doses of up to 20 mg, THC produces effects on mood, memory, motor
coordination, cognitive ability, sensorium, time sense, and self-perception. There
is an increased sense of well-being or euphoria accompanied by feelings of
relaxation or sleepiness when subjects are alone. With greater intake of THC,
short-term memory is impaired, and the capacity to carry out tasks that require
multiple mental steps to reach a specific goal deteriorates. This effect on
memory-dependent, goal-directed behavior has been called temporal
disintegration and is correlated with a tendency to confuse past, present, and
future. Depersonalization, a sense of strangeness and unreality about one’s self,
may also occur. Marijuana smokers often report a voracious appetite (the
“munchies”), dry mouth and throat, more vivid visual imagery, and a keener
sense of hearing. Altered time perception is a consistent effect of cannabinoids, so
minutes seem like hours. Larger doses of THC can produce frank hallucinations,
delusions, and paranoid feelings. Thinking becomes confused and disorganized.
Anxiety that reaches panic proportions may replace euphoria, often as a feeling
that the drug-induced state will never end. Because of the rapid onset of effects
when marijuana is smoked, most users can regulate their intake to avoid the
excessive doses that produce these unpleasant effects. Marijuana may cause an
acute exacerbation of symptoms in stabilized schizophrenics. Clinical findings on
examination may include tachycardia, hypertension, and marked conjunctival
injection. Chronic smoking of marijuana and hashish is associated with bronchitis
and asthma, even though THC is a mild bronchodilator.
