Various factors influence the specific effects of any given THC blood concentration. These include the experience of the user and the individual vulnerability of the user to psychoactive reactions. Also important are the expectations of the user as to the effects of marijuana and the setting of its use.
Most of the effects of marijuana on behavior disappear within three to five hours after the beginning of use. The more complex and difficult the skill, the more likely marijuana will reduce ability. Selective attention is the ability to disregard irrelevant information. Long-term users have reduced selective attention, even after they quit using the drug. Similarly, increased frequency of marijuana use impairs information processing speed. The use of marijuana along with drinking alcohol may cause much greater impairment than either substance alone. Carisoprodol is a central nervous system depressant that is prescribed to relax muscles.
Meprobamate is also a central nervous system depressant. Either of these drugs reduces visual functioning, slow thinking and cause confusion. Also disorients, reduces comprehension, and causes sluggish movements, tremor, and loss of coordination. The effects of carisoprodol begin within half an hour. It appears that single doses of carisoprodol do not effect thinking ability or psychomotor performance. However, single doses of meprobamate can impair the ability to divide attention, slow reflexes, and impair coordination. The effects of driving under the influence of either carisoprodol or meprobamate include sleepiness, inattentiveness and slow responses. Also poor perception, slower reaction time, confusion, disorientation and slurred speech. In addition, it causes lack of coordination and difficulty standing, walking or exiting vehicles. The use of other central system depressants can increase impairment. For example, drinking alcohol increases the sedation and confusion that carisoprodol can cause. It also increases the sleepiness, confusion, incoherence and disorientation that meprobamate can cause. Cocaine is a powerful central nervous system stimulant. It increases alertness, reduces fatigue, improves mental focus and enhances mental clarity. It also improves the performance of some simple tasks, creates euphoria, and creates feelings of well-being and strength. At higher doses, cocaine can cause mental confusion, disorientation, fear, paranoia, aggression, delusions, hallucinations, and lead to anti-social behavior. Some researchers have found no effect of cocaine on thinking or psychomotor performance. However, others have found cocaine to enhance attention, learning, and psychomotor performance. Cocaine reduces the negative effects on performance of sleep deprivation or alcohol intoxication. The over-the-counter drug dextromethorphan reduces coughs from minor throat and bronchial irritation. Recreationally it raises mood, increases perceptual awareness and creates euphoria. It also can create dream-like experiences and a sense of separation of the mind from the body. Negative effects from taking recommended doses of dextromethorphan are rare. However, slight drowsiness and dizziness can occur. Taking higher doses for recreational reasons can lead to disorientation, confusion, reduced memory and impaired judgment.
It can also lead to psychomotor impairment, distorted perception of time, and hallucinations of both sight and sound.
Combining dextromethorphan with promethazine can cause great drowsiness or impair the mental or physical abilities needed to drive safely. Recreationally it’s a sedative and it also enhances the effects of alcohol or opioids. Cocaine users sometimes use it to increase the level at which seizures occur.