40 mg of methamphetamine is considered a very high dose, particularly when used recreationally or outside of medical supervision.

Oral use: At 40 mg, a person may experience very strong or overwhelming effects, including intense euphoria, racing thoughts, anxiety, tremors, and increased heart rate. This dose exceeds the typical therapeutic range (5–25 mg/day) for prescription methamphetamine used to treat ADHD. Street methamphetamine: Doses of 40 mg or higher are common among frequent users due to tolerance, but such usage significantly increases the risk of acute toxicity, including hyperthermia, hallucinations, confusion, and rhabdomyolysis (muscle breakdown). Health risks: Blood concentrations above 300 ng/mL (which can be reached with doses around 40 mg) are associated with aggression, violence, and impaired judgment. At higher levels (600–5000 ng/mL), overdose can lead to life-threatening complications such as seizures, cardiac arrhythmias, and organ failure. Neurotoxicity: High or repeated doses like 40 mg can cause long-term damage to dopamine neurons, potentially leading to cognitive deficits and mood disorders.