Barbiturates

Barbiturates were introduced in the early 20th century and became the dominant sedatives and sleep medicines for decades, as well as early anticonvulsants. Because they slow brain activity, they were prescribed for anxiety, insomnia, and seizures, and are still used in surgery and to treat epilepsy (phenobarbital in particular). From the 1960s onward they were largely displaced by benzodiazepines, which achieve similar calming effects with a far lower risk of fatal overdose. Barbiturates vary widely in how fast they act and how long they last, from ultra-short-acting anesthetics to long-acting anticonvulsants.

Barbiturates are nonselective CNS depressants that enhance the activity of gamma-aminobutyric acid (GABA), the brain's main inhibitory neurotransmitter, at the GABA-A receptor. By increasing GABA-driven inhibition, they reduce the excitability of neurons throughout the brain, producing sedation at low doses and progressively deeper CNS depression as the dose rises. Unlike benzodiazepines — which only amplify GABA's own signal — barbiturates can at higher doses directly prolong the opening of the chloride channel even without GABA present, which is a major reason their overdose risk is higher: there is no ceiling to the depression they can cause, so high doses lead to coma, suppressed breathing, and death.

At low doses barbiturates produce drowsiness, reduced anxiety, mild euphoria, and relaxation; higher doses cause slurred speech, impaired coordination, confusion, and heavy sedation. Because tolerance to the sedative effect develops faster than tolerance to the dose that suppresses breathing, a person using barbiturates repeatedly needs steadily larger amounts for the same effect while the lethal dose stays roughly fixed — so the margin of safety shrinks with continued use. This is a defining hazard of the class and a key difference from benzodiazepines.

Barbiturates are among the more dangerous CNS depressants because their therapeutic window is narrow: the dose that produces the desired effect is close to the dose that suppresses breathing. Overdose slows or stops breathing, reducing oxygen to the brain (hypoxia), which can cause coma, permanent brain damage, or death — and there is no specific antidote as there is for opioids. The danger multiplies when barbiturates are combined with other CNS depressants such as alcohol, opioids, or benzodiazepines, a common cause of fatal overdose. The second major hazard is withdrawal: regular use produces physical dependence, and unlike benzodiazepine withdrawal — which is rarely life-threatening on its own — withdrawal from prolonged barbiturate use can be genuinely life-threatening, causing seizures, delirium, and death. For this reason barbiturates must never be stopped abruptly; discontinuation requires a medically supervised taper. Long-term use is also associated with tolerance, dependence, and cognitive impairment.