Medlock Holmes is summoned to investigate a city that never seems to sleep. The streets remain alive long after midnight. Factories work around the clock. Students study without rest. Traders chase impossible fortunes. Artists paint through the night. Everyone appears driven by an invisible force that promises endless energy, relentless focus, and extraordinary productivity. Yet Holmes quickly notices another pattern. The faster the city moves, the more fragile it becomes. People who once brimmed with confidence now pace the streets in terror. Windows are barricaded against imagined enemies. Brilliant careers collapse into paranoia. Bodies begin to fail long before minds are willing to stop. Holmes soon realises that he is confronting the world of stimulant-related disorders. Stimulants-including cocaine, amphetamines, methamphetamine, prescription stimulants such as methylphenidate, and newer synthetic cathinones (”bath salts”)-all share a common feature: they dramatically increase alertness, energy, confidence, and reward by enhancing dopaminergic neurotransmission. Although they differ chemically, they converge upon the brain’s reward circuitry, particularly the dopamine pathways linking the ventral tegmental area to the nucleus accumbens. Unlike alcohol, whose effects slow the nervous system, stimulants accelerate it. The heart races. Blood pressure rises. Sleep disappears. Thoughts accelerate. Confidence grows. For a time, the world feels conquerable. But Holmes knows that every borrowed advantage eventually demands repayment. The chapter explores how stimulant use disorder develops through powerful reinforcement learning. Each episode of stimulant use floods the brain with dopamine, strengthening memories that connect pleasure with the drug, the environment, the people present, and even particular times of day. Gradually, everyday rewards lose their appeal while drug-associated cues become increasingly irresistible. Craving is no longer simply desire-it becomes conditioned biology. Holmes becomes fascinated by the distinction between positive and negative reinforcement. Initially, stimulants are taken because they produce euphoria, energy, confidence, and reward. Later, they are increasingly used simply to escape exhaustion, dysphoria, emotional emptiness, and overwhelming craving. The pursuit of pleasure quietly transforms into avoidance of suffering. As Holmes interviews those affected, another pattern emerges. Not everyone uses stimulants in the same way. Some binge for days before crashing. Others remain abstinent for weeks between episodes. Some use prescription medications appropriately throughout life without developing addiction. The disorder is defined not by the drug itself, but by the progressive loss of control despite mounting harm. DSM-5 therefore focuses on impaired control, craving, hazardous use, tolerance, withdrawal, and continued use despite significant consequences, with severity ranging from mild to severe depending upon the number of criteria met. The investigation then turns towards intoxication. Holmes watches an apparently confident businessman become increasingly suspicious. Every passing stranger appears threatening. Ordinary sounds become sinister. Minor coincidences seem like evidence of elaborate conspiracies. He learns that stimulant intoxication may progress from heightened confidence to severe paranoia, hallucinations, agitation, seizures, cardiac arrhythmias, hyperthermia, and even sudden death. Methamphetamine-induced psychosis may persist longer than cocaine-induced psychosis and sometimes becomes difficult to distinguish from primary schizophrenia, requiring careful longitudinal assessment. Eventually every binge ends. The crash arrives. Energy vanishes. Mood collapses. Sleep returns in overwhelming waves. Pleasure disappears. The chapter explains stimulant withdrawal as a state of profound dopamine depletion, characterised by fatigue, dysphoria, hypersomnia, increased appetite, vivid dreams, slowed thinking, and intense craving. Although rarely medically dangerous in itself, withdrawal may be accompanied by severe depression and suicidal thinking, making careful psychiatric assessment essential. Holmes also uncovers the extensive medical consequences hidden beneath the surface. Stimulants constrict blood vessels while increasing heart rate and blood pressure. The result may be myocardial infarction, stroke, cardiomyopathy, aortic dissection, seizures, cognitive impairment, and, particularly with methamphetamine, long-term neurotoxicity and increased risk of Parkinson disease. Repeated intranasal cocaine use damages nasal tissues, while chronic methamphetamine use produces the devastating dental destruction commonly known as “meth mouth.” The final lesson concerns treatment. Unlike alcohol or opioid withdrawal, stimulant withdrawal rarely requires complex medical detoxification. Instead, recovery depends upon rebuilding behaviour. Holmes finds that the strongest evidence supports psychological interventions rather than medication alone. Contingency management consistently produces the best outcomes by rewarding abstinence and treatment engagement. Cognitive behavioural therapy helps patients recognise triggers, manage cravings, and develop healthier coping strategies, while twelve-step programmes and community support provide long-term reinforcement for recovery. Although numerous medications have been studied, none has yet become an established first-line pharmacological treatment. As Holmes prepares to leave the sleepless city, dawn finally breaks. The streets grow quieter. For the first time, people begin to rest. He reflects that the greatest illusion stimulants create is not unlimited energy-it is the belief that human beings can permanently outrun the biological limits of the brain. Eventually, every borrowed hour must be repaid. Recovery begins not by running faster, but by learning once again how to stop. Key Takeaways * Stimulants include cocaine, amphetamines, methamphetamine, prescription stimulants, and synthetic cathinones. * They primarily act by increasing dopamine transmission within the brain’s reward pathways. * Stimulant use disorder is characterised by impaired control, craving, and continued use despite harm. * Intoxication may cause euphoria, insomnia, hypertension, agitation, paranoia, hallucinations, and cardiovascular emergencies. * Withdrawal typically produces fatigue, depression, hypersomnia, increased appetite, and intense craving. * Chronic stimulant use alters learning, memory, executive functioning, and reward processing. * Methamphetamine use is associated with neurotoxicity, cognitive impairment, and increased Parkinson disease risk. * Stimulant-induced psychosis may resemble primary psychotic disorders and requires careful longitudinal assessment. * Contingency management has the strongest evidence among psychosocial treatments, supported by CBT and mutual-help programmes. * No medication has yet become an established first-line treatment for stimulant use disorder. 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