Speed, the street name for amphetamine, floods the brain with chemical messengers that control alertness, pleasure, and motivation. The result is a surge of energy, heightened focus, and euphoria that can last four to six hours with a single oral dose. But the drug also pushes the heart, body temperature, and appetite into overdrive, and chronic use can damage cognition and mental health in ways that persist long after the drug wears off.
How Speed Works in the Brain
Amphetamine’s core action is forcing nerve cells to release large amounts of dopamine and norepinephrine, two chemical messengers that regulate mood, attention, and the body’s fight-or-flight response. Most drugs that affect these systems simply block their recycling. Amphetamine does that too, but its signature move is more aggressive: it actually reverses the pumps that normally pull these chemicals back into the nerve cell, pushing them outward into the gaps between neurons. The combined effect raises levels of dopamine and norepinephrine far higher than normal brain activity ever would.
Dopamine is the chemical most associated with reward and motivation. When speed artificially spikes dopamine, the brain registers it as an intensely pleasurable, important event. That’s what produces the rush of euphoria. Norepinephrine, meanwhile, ramps up heart rate, blood pressure, and alertness. Together, these two surges account for virtually every effect the drug produces, from the initial high to the cardiovascular strain.
What the High Feels Like
The immediate experience of taking speed includes a heightened sense of well-being, excitement, and mental sharpness, along with increased energy and talkativeness. Many users report feeling hypersensitive to sights, sounds, and touch. Higher doses intensify the feelings of wakefulness, mania, and euphoria. SAMHSA describes the state as resembling a manic episode.
The cognitive picture is more nuanced than users might expect. Research reviews show that amphetamine does improve attention in healthy people, with roughly half of controlled studies confirming that effect. But benefits to higher-level thinking, like flexible problem-solving and decision-making, are inconsistent. The perception that speed makes you smarter is largely the drug boosting confidence and motivation rather than raw intellectual ability.
Personality also shapes the experience. People with high trait impulsivity tend to feel stronger euphoria and arousal. Those with lower sensation-seeking tendencies may actually feel less energetic on the drug, not more. So two people taking the same dose can have genuinely different experiences.
Effects on the Heart and Body
Speed puts immediate stress on the cardiovascular system. A large meta-analysis covering more than 10,000 participants found that amphetamines raise systolic blood pressure by about 2 mmHg, diastolic blood pressure by roughly the same amount, and heart rate by nearly 4 beats per minute on average. Those numbers sound modest, but they represent averages across therapeutic doses. Recreational doses are often much higher, and the effect scales up accordingly.
At toxic levels, the cardiovascular strain becomes dangerous. Complications from a speed overdose can include dangerously high body temperature, seizures, hemorrhagic stroke, abnormal heart rhythms, aortic dissection, and acute kidney injury. There is no ceiling effect with amphetamine toxicity, meaning the danger keeps climbing with the dose.
Speed also suppresses appetite, sometimes dramatically. People on binges may go days without eating, leading to dehydration and significant weight loss. The drug’s effect on body temperature is complex: animal research shows amphetamine actually alters how the body manages heat during exertion, slowing the initial rise in core temperature but potentially impairing the body’s ability to recognize overheating, which is why hyperthermia is a hallmark of overdose, especially in hot environments like clubs or festivals.
How Long It Lasts
When swallowed, speed reaches peak blood concentration in about three hours, and the effects of an immediate-release dose typically last four to six hours. Extended-release pharmaceutical versions peak around seven hours and last eight to twelve. Snorting or smoking the drug shortens the time to onset considerably, producing a faster, more intense but shorter-lived high. The comedown, marked by fatigue, irritability, and low mood, often begins within hours of the peak wearing off and can linger for a day or more after a single use.
What Chronic Use Does to the Brain
Repeated amphetamine use gradually erodes the cognitive abilities that drew many users to the drug in the first place. Long-term users show measurable declines across multiple domains: attention, memory, decision-making, impulse control, mental flexibility, and psychomotor speed. These deficits mirror the pattern seen in chronic cocaine users, suggesting a common pathway of stimulant-driven brain damage.
The psychological toll extends further. Chronic use and withdrawal can trigger paranoia, psychosis (including hallucinations and delusions), depression, and suicidal thinking. Stimulant psychosis can closely resemble schizophrenia and sometimes requires hospitalization. For some people, psychotic symptoms can recur even after long periods of abstinence, especially under stress.
Withdrawal Timeline
Stopping speed after regular use triggers a withdrawal process that unfolds in stages. During the first two to three days, symptoms peak: deep fatigue, depression, anxiety, irritability, body aches, headaches, intense cravings, and long stretches of sleep. The worst of these symptoms usually resolve within four to seven days.
Over the next two to three weeks, most people stabilize enough to handle daily activities. Mood begins to normalize, though brief episodes of craving can strike unpredictably. Many people experience vivid “drug dreams” during this phase, dreaming of using speed in such realistic detail that they wake up anxious and craving.
After about a month, a subtler phase sets in. Mild cognitive dullness, memory difficulties, moderate depression, and ongoing cravings can persist for weeks or months. Executive function, the ability to plan, organize, and control impulses, is typically the slowest to recover.
Medical Uses of Amphetamine
Amphetamine is not only a street drug. Pharmaceutical versions are FDA-approved for ADHD and narcolepsy, prescribed at carefully controlled doses. For ADHD in children six and older, treatment typically starts at 5 mg once or twice daily and rarely exceeds 40 mg per day. For narcolepsy, the therapeutic range is 5 to 60 mg daily. At these doses, the drug improves attention, alertness, and energy without producing the intense euphoria associated with recreational use.
The distinction between medical and recreational use largely comes down to dose, route, and pattern. A person taking a prescribed low oral dose on a consistent schedule experiences a steady, moderate increase in focus. A person snorting or injecting large amounts gets a rapid dopamine spike that drives euphoria, compulsive re-dosing, and the cycle of tolerance and dependence.
Dangerous Combinations
Certain substances and health conditions make speed especially risky. Combining amphetamine with a class of older antidepressants called MAOIs can trigger a hypertensive crisis, a sudden, life-threatening spike in blood pressure. This risk persists for up to 14 days after stopping an MAOI. Mixing speed with other drugs that raise serotonin levels, including some common antidepressants, increases the risk of serotonin syndrome, a potentially fatal condition involving high fever, agitation, and muscle rigidity.
People with pre-existing heart disease, severe high blood pressure, overactive thyroid, or glaucoma face amplified danger from even moderate doses. The stimulant load on an already compromised cardiovascular system can push the body past its ability to compensate.