Amphetamine Pharmacokinetics
The long half-life (~10–11h) is the central harm reduction message. Set the time axis to 36h and see exactly what is still in your system the next morning, afternoon, and evening.
Compound
Vitamin C acidifies urine and speeds amphetamine elimination by ~50% (methamphetamine elimination by ~20%). The blue dashed line shows the curve with vitamin C supplementation. This is a documented harm reduction strategy — it does not eliminate risk but reduces duration.
Dose schedule
pH-dependent elimination: Amphetamine is a weak base (pKa 9.9). In acidic urine, more is in the ionised form and cannot be reabsorbed — elimination rate increases substantially. Vitamin C (ascorbic acid) acidifies urine and can reduce t½ by ~30–50%. Alkaline urine (baking soda, antacids) does the opposite — extending duration and increasing plasma levels. The blue dashed curve shows the vitamin C effect.
Methamphetamine vs amphetamine: Similar t½ but meth produces roughly 3× more dopamine release per unit plasma concentration and has greater CNS penetration. This means greater euphoria, greater cardiovascular strain, and greater neurotoxicity risk at equivalent plasma levels. The effect zones are scaled accordingly.
Dangerous combinations
Hypertensive crisis and serotonin syndrome. Amphetamines cause massive monoamine release — MAOIs prevent their breakdown. Can be fatal within minutes. Never combine under any circumstances. Includes some antidepressants and linezolid.
Additive and potentially synergistic cardiovascular strain. Combined tachycardia, hypertension, and hyperthermia. Substantially increases risk of cardiac events and stroke.
Unpredictable interaction. Lithium can reduce stimulant effects (leading to dose escalation) but also increases serotonergic effects. Serious toxicity risk.
Amphetamine masks alcohol intoxication — people drink far more than they realise. The stimulant effect wears off before the alcohol does, causing sudden severe intoxication. Cardiovascular strain from both substances.
Combined cardiovascular strain from stimulant + anaesthetic. Amphetamine can mask ketamine sedation, leading to redosing. Disorientation and inability to assess own condition significantly increased.
Increased anxiety and paranoia. Cannabis used to "take the edge off" stimulant effects can unpredictably amplify anxiety instead. Cardiovascular effects additive.
Acidic urine significantly speeds amphetamine elimination. Vitamin C supplementation is used as a harm reduction strategy to reduce duration and help comedown. Toggle the "Vitamin C" option to see the effect modelled.