13. Feb, 2015


The subject of the effectiveness of dexamphetamine (dex) comes up regularly in the Idiopathic Hypersomnia and Narcolepsy community so we thought we would share some fairly standard information with you that your doctor may have failed to mention when prescribing dex.

Is your diet particularly acidic? Acidic foods (including vitamin C supplements) decrease the absorption of dex, reducing its effect. Acidic foods also tend to make urine more acidic too, which increases the rate dex is released from the body, again decreasing the effectiveness. Normally around 30% of all dex you take is excreted in the urine. However highly acidic urine (around pH 4-5) will result in as much as 75% of the dex being eliminated from the body! That would make a huge difference to the effectiveness of dex, whereas a low acid or alkaline urine (around pH 8) will result in less than 5% of dex being eliminated via your urine.

Antacids like Rennies or Tumms help alkaline stomach acid, so too does simple bicarbonate soda - because even on an empty stomach the absorption of dex can be reduced. Just thinking about food produces gastric acid which has a very low pH.

Dexamphetamine is a finicky medication, it is more effective when you are hydrated so drink plenty of water (not soft drinks, fruit juice or caffeine drinks as these are all highly acidic - sorry guys so too is chocolate) and do not take it with food. The general timeframe is to take dex at least 45min before food and no sooner than 2 hours after food. It is also best to avoid alcohol.

You will find many different Acidic/Alkaline food lists online to help you choose better food options and if you want to check the pH level of your urine you can pick up pH test strips from your chemist rather cheaply. Make sure you speak to your doctor about getting the best out of your medication and ALWAYS remember to tell all of your treating doctors what medication you are already taking (don't assume they know). Dex interacts with various vitamins/minerals and medications - including some very common antidepressants.

Acidifying Agents:

Gastrointestinal acidifying agents (guanethidine, reserpine, glutamic acid hydrochloride, ascorbic acid, fruit juices etc) lower absorption of amphetamines. Urinary acidifying agents (ammonium chloride, sodium acid phosphate etc) increase the concentration of the ionised species of the amphetamine molecule, thereby increasing urinary excretion. Both groups of agents lower blood levels and the efficacy of amphetamines.

Alkalising Agents:

Gastrointestinal alkalising agents (sodium bicarbonate etc) increase absorption of amphetamines. Urinary alkalising agents (acetazolamide and some thiazides) increase the concentration of the non-ionised species of the amphetamine molecule thereby decreasing urinary excretion.

Dexamphetamine Product Information

For more technical reading on drug metabolism

Urinary excretion of d-amphetamine following oral doses in humans: implications for urine drug testing

Subjective responses and excretion patterns of dextroamphetamine after the administration of therapeutic doses.

Duration of Detectable Methamphetamine and Amphetamine Excretion in Urine after Controlled Oral Administration of Methamphetamine to Humans