A considerable number of individuals using benzodiazepines for insomnia escalate their dosage, sometimes above therapeutically-prescribed dose levels. Tolerance to the anxiolytic effect of benzodiazepines has been clearly demonstrated in rats. In humans, there is little evidence that benzodiazepines retain their anti-anxiety effects beyond four months of continuous treatment; there is evidence that suggests that long-term use of benzodiazepines may actually worsen anxiety, which in turn may lead to dosage escalation, with one study finding 25% of patients escalated their dosage. Some authors, however, consider benzodiazepines to be effective long-term; however, it is more likely that the drugs are acting to prevent rebound anxiety withdrawal effects which can be mistaken as continued drug efficacy. Tolerance to the anticonvulsant and muscle-relaxing effects of benzodiazepines occurs within a few weeks in most patients. Risk factors
The risk factors for benzodiazepine dependence are long-term use beyond four weeks, use of high doses, use of potent short-acting benzodiazepines, dependent personalities, and proclivity for substance use. Use of short-acting benzodiazepines leads to repeated withdrawal effects that are alleviated by the next dose, which reinforce in the individual the dependence. A physical dependence develops more quickly with higher potency benzodiazepines such as alprazolam (Xanax) than with lower potency benzodiazepines such as chlordiazepoxide (Librium).Symptom severity is worse with the use of high doses, or with benzodiazepines of high potency or short half-life. Other cross-tolerant sedative hypnotics, such as barbiturates or alcohol, increase the risk of benzodiazepine dependence. Similar to opioids use for pain, therapeutic use of benzodiazepines rarely leads to a substance use disorder.
In normal subjects, increases in growth hormone occurs, whereas, in benzodiazepine-tolerant individuals, this effect is blunted.Animal studies have shown that repeated withdrawal from benzodiazepines leads to increasingly severe withdrawal symptoms, including an increased risk of seizures; this phenomenon is known as kindling. Kindling phenomena are well established for repeated ethanol (alcohol) withdrawal; alcohol has a very similar mechanism of tolerance and withdrawal to benzodiazepines, involving the GABAA, NMDA, and AMPA receptors.The shift of benzodiazepine receptors to an inverse agonist state after chronic treatment leads the brain to be more sensitive to excitatory drugs or stimuli. Excessive glutamate activity can result in excitotoxicity, which may result in neurodegeneration. The glutamate receptor subtype NMDA is well known for its role in causing excito-neurotoxicity. The glutamate receptor subtype AMPA is believed to play an important role in neuronal kindling as well as excitotoxicity during withdrawal from alcohol as well as benzodiazepines. It is highly possible that NMDA receptors are involved in the tolerance to some effects of benzodiazepines.Animal studies have found that glutamergic changes as a result of benzodiazepine use are responsible for a delayed withdrawal syndrome, which in mice peaks 3 days after cessation of benzodiazepines. This was demonstrated by the ability to avoid the withdrawal syndrome by the administration of AMPA antagonists. It is believed that different glutamate subreceptors, e.g., NMDA and AMPA, are responsible for different stages/time points of the withdrawal syndrome. NMDA receptors are upregulated in the brain as a result of benzodiazepine tolerance. AMPA receptors are also involved in benzodiazepine tolerance and withdrawal.