How long does speed work, and what are amphetamine's side effects?

The rush from speed is usually over within a few hours. In adults, the elimination half-life of amphetamine sits around 10 to 12 hours, with plasma levels peaking 2 to 3 hours after intake (PMID 28910145). Your body is therefore still busy with a substance you stopped feeling long ago.

I find that the most underrated number around speed.

The lab also measures something other than your feeling. And how long the lab still sees the drug depends, in part, on the acidity of your urine.

How long does speed work?

For most people the noticeable effect of speed lasts roughly four to eight hours. Blood levels peak 2 to 3 hours after intake with an immediate-release form (PMID 28910145). After that the effect flattens out while the substance itself keeps circulating for hours. Duration of effect and presence in the body are not the same thing.

That gap explains a lot. You can feel entirely sober and still have a body that is processing amphetamine.

In children the half-life is shorter, around 7 hours (PMID 28910145). That shows how much age and physiology shift these numbers.

What are the effects of speed on your body?

Amphetamine is a sympathomimetic: it imitates the response of your own stress system. It pushes up heart rate, raises blood pressure, widens the pupils, suppresses appetite and postpones sleep. The alertness you experience is that same response, simply seen from its pleasant side.

The effects of speed are not separate items. They are one response with several faces.

The Dutch national institute RIVM tracks, through national drug monitoring, how often amphetamine is used in the Netherlands and which incidents are reported. Amphetamine has featured among the more frequently reported substances for years.

What side effects does amphetamine have on the heart and blood pressure?

Even in controlled medical use, amphetamines raise resting heart rate and blood pressure modestly but measurably (PMID 32792083). That same review describes reports of arrhythmias, cardiomyopathy and sudden cardiac death, while stressing that isolated reports do not prove causation. With street speed, the dose and the purity are unknown on top of that.

That last point is not a detail. An unknown dose makes a modest cardiac effect hard to predict.

Sleep and appetite are the two systems people usually notice next. Both can need days to return.

Why does the comedown feel heavier than the high?

The comedown lags behind the pharmacology. While the substance is still being excreted, your sleep debt, your appetite and your mood recover at a far slower pace. After a single night people often describe two to three days of fatigue, irritability and a flat, empty feeling. That stretch usually outlasts the high itself.

Repeat use to soften that dip is the route along which an amphetamine addiction tends to build. I prefer to call that a pattern rather than a character trait.

A test says nothing about it either way. A lab value shows exposure, not dependence.

Why does your urine pH change how long amphetamine stays detectable?

Amphetamine is a base. That means the acidity of your urine helps decide how much your kidneys actually excrete and how much is reabsorbed into the blood. In acidic urine the drug clears faster; in alkaline urine elimination takes longer (PMID 25157, PMID 32198137). This is why no single fixed detection window exists.

In amphetamine-type stimulants, half-life, residence time in the body and blood exposure all rose clearly as urine became more alkaline (PMID 18481797). Acidic urine speeds clearance up instead.

The urinary half-life of amphetamine itself was around 21 hours in one controlled study, with 40 to 58 percent of the dose recovered in urine (PMID 15570192).

That last row is why two people with identical use can end up with a different result.

Take two men who use the same amount of speed on a Saturday night and are both tested 36 hours later. One drinks plenty of water in the days after and naturally has fairly acidic urine. The other does not. On Monday morning the lab measures 250 ng/ml for the first and 1,100 ng/ml for the second.

Same substance, same amount, same night.

The difference lies in the acidity of their urine, not in what they took. That is why the question of how long speed stays detectable has no single answer that holds for everyone.

What is the difference between street speed and dexamfetamine?

Chemically they are close relatives; pharmaceutically they are not. Dexamfetamine appears in the Dutch Farmacotherapeutisch Kompas as a registered medicine, with a fixed strength, a patient leaflet and medical supervision. Street speed has none of those three: purity varies per batch and adulterants are invisible. That difference is the heart of the comparison.

An immunoassay screen responds to the amphetamine class, not to where the substance came from. GC-MS confirmation names the compound precisely, yet still says nothing about its source.

So someone with a prescription and someone with a gram from the market can produce the same result.

What a lab value does and does not tell you here

A positive result means exposure within a certain window. It does not say how much you used, not exactly when, and not whether dependence is present. That is the honest limit of this kind of measurement, and I would rather name that limit myself than let you find it later.

If you want to know whether amphetamine is still measurable in your case, you can book an amphetamine screening blood test without a doctor's referral.

The concrete windows per matrix are set out in how long amphetamine stays detectable. The wider frame, duration of effect next to detection window across substances, sits in how long drugs work. For two other stimulants with a very different comedown, read what cocaine does to your body and 3-MMC effects and the comedown. Why the threshold itself shifts the window is explained in what a cut-off value is.

I would turn the question around. Not how long it stays detectable, but how long your heart, your sleep and your appetite are still recovering.

Every blood test result at Zuivertest includes a professional assessment by a BIG-registered doctor. Discuss your results with your GP before making treatment decisions.

Sources

• Markowitz J.S., Patrick K.S., "The Clinical Pharmacokinetics of Amphetamines Utilized in the Treatment of Attention-Deficit/Hyperactivity Disorder", Journal of Child and Adolescent Psychopharmacology, 2017 (PMID 28910145)
• Torres-Acosta N. et al., "Cardiovascular Effects of ADHD Therapies: JACC Review Topic of the Week", Journal of the American College of Cardiology, 2020 (PMID 32792083)
• Huang W., Czuba L.C., Isoherranen N., "Mechanistic PBPK Modeling of Urine pH Effect on Renal and Systemic Disposition of Methamphetamine and Amphetamine", Journal of Pharmacology and Experimental Therapeutics, 2020 (PMID 32198137)
• Wan S.H., Matin S.B., Azarnoff D.L., "Kinetics, salivary excretion of amphetamine isomers, and effect of urinary pH", Clinical Pharmacology and Therapeutics, 1978 (PMID 25157)
• Wang L. et al., "Influences of urinary pH on the pharmacokinetics of three amphetamine-type stimulants using a new high-performance liquid chromatographic method", Journal of Pharmaceutical Sciences, 2009 (PMID 18481797)
• Kim I. et al., "Urinary pharmacokinetics of methamphetamine and its metabolite, amphetamine following controlled oral administration to humans", Therapeutic Drug Monitoring, 2004 (PMID 15570192)
• Farmacotherapeutisch Kompas, dexamfetamine monograph (farmacotherapeutischkompas.nl)
• RIVM, Dutch national drug monitoring and incident registration (rivm.nl)