Treating MCS with dextromethorphan


Martin Pall’s book, Explaining “Unexplained Illnesses”, and the treatment protocols based on his NO/ONOO- (nitric oxide/peroxynitrite) cycle theory, mainly focus on using nutritional supplements for treatment. However, Pall mentions a number of medications that act as NMDA antagonists and are already or may in future be used to treat MCS and/or other multisystem illnesses. One of these is dextromethorphan which is available in over-the-counter cough suppressant medications.

Dr Donald Dudley reported in ‘MCS: trial by science’ that dextromethorphan hydrobromide

does significantly decrease symptoms on olfactory exposure to volatile short-chain carbon compounds in MCS patients. It has been used by the author in more than 30 of these patients with significant positive effect.

Pall reports in Explaining “Unexplained Illnesses” that a number of physicians in Washington State have observed similar responses, and of the six MCS patients who had tried dextromethorphan that he spoke to, five had found it stopped or decreased symptoms. Some people with MCS don’t tolerate the normal dose. However, some of these people do tolerate and benefit from half or a quarter of the adult dose.

Metabolism of dextromethorphan depends on the enzyme CYP2D6, which is one of the most polymorphic of the cytochrome P450 enzymes. This means that there are genetic differences in people’s metabolism of dextromethorphan and how effective and safe they find it. You can read more about how it is metabolized here.

It’s important to note that they are talking about taking dextromethorphan when chemical exposures occur, not on a regular basis.

Dextromethorphan has also been found to reduce neuropathic pain and pain caused by fibromyalgia.

Not safe for everyone
While dextromethorphan is considered safe enough to make available without prescription, according to the Therapeutic Goods Administration (Australia) some people should not take it, or should be cautious, because of their medical condition or because it interacts with another medication they take. You can read the TGA information here. You can also check with your doctor or pharmacist whether it is safe for you to try.

Side effects and overdose symptoms
The TGA says:

Side effects with usual doses are uncommon but may include mild drowsiness, fatigue, dystonias, dizziness and gastrointestinal disturbances (nausea or vomiting, stomach discomfort, or constipation). Side effects that may occur with high doses (overdosage) include excitation, confusion, psychosis, nervousness, irritability, restlessness, “serotonin syndrome”, severe nausea and vomiting, and respiratory depression.

At high doses dextromethorphan has a similar effect to phencyclidine (PCP) and ketamine. In the US there is concern about people using it as a recreational drug and deaths have been reported. The US National Drug Intelligence Center says:

Acute dosages (between 250 and 1,500 milligrams) can cause blurred vision, body itching, rash, sweating, fever, hypertension, shallow respiration, diarrhea, toxic psychosis, coma, and an increase in heart rate, blood pressure, and body temperature. Some abusers become violent after ingesting the drug. Little is known about the long-term effects of DXM abuse; however, anecdotal reporting and limited clinical research suggest that extensive and prolonged abuse may cause learning and memory impairment.

There are reports of addiction but this is generally thought to be psychological, not physical.

My experience
Most of the cough medicines containing dextromethorphan contain other active ingredients such as antihistamines. They all contain artificial colours, flavours and sweeteners, which I normally avoid. The formulation that looked and smelled least worst to me was a lozenge. I’ve had allergic and adverse reactions to many medications and various food additives, so I was very doubtful about being able to tolerate dextromethorphan. I tried about a tenth of a lozenge first. That test went okay so the next time I was exposed to fragrance I tried half a lozenge. This reduced my usual reaction to fragrance and a whole lozenge (a child’s dose) stopped it. I did have some mild symptoms afterwards and I don’t know whether they were caused by the original exposure, the dextromethorphan or the other ingredients, but I felt much better than I had after similar fragrance exposures without dextromethorphan. Dextromethorphan has stopped or reduced some of my reactions to other chemicals that I’m sensitive to, but I haven’t found it effective against all of them. However, the results with fragrance alone make dextromethorphan very useful to me. When an exposure is predictable I take it about half an hour before – this prevents reactions from starting.

Since I first tried dextromethorphan a few years ago I’ve become less sensitive to fragrance and other chemicals. I still find avoidance the best strategy, but for the times when I can’t do that I’ve found more nutritional supplements that are useful for reducing reactions. I rarely take dextromethorphan now. However, I am still glad that I can take it when I am exposed to a lot of fragrance or other chemicals.

Dextromethorphan is more readily available and much cheaper than the nutritional supplements some people with MCS find very effective. Unfortunately the lozenges I have taken in the past have gone off the market and the only one available here now contains an ingredient I’ve had bad reactions to. I haven’t run out of the old brand yet and I’ve been using so few that maybe by the time I finished them there will be a new, more tolerable brand available. Maybe one day someone will wake up to the fact that there is a large potential market for a low dose dextromethorphan product free from artificial colours, flavours, sweeteners, preservatives and other additives.

Where possible I have included links to sources and/or further information in the text. The two books I have referred to are:
Pall, M.L. (2007) Explaining “Unexplained Illnesses” Haworth Press, New Yorkare:
Dudley D.L. (1998) MCS: trial by science. In Defining Multiple Chemical Sensitivity (Matthews, B.L., ed.), pp 9-26, McFarland & Company, Jefferson, North Carolina.

An earlier version of this article appeared in Sensitivity Matters December 2009

Disclaimer: I am not a doctor or health professional and this is not medical advice. For medical advice about whether dextromethorphan is appropriate for you ask a doctor.



  1. Catherine Hollingsworth

    I don’t handle the Dextromethorphan well, either. However upon understanding the process of Dr. Pall’s research – and taking his supplements – I have also discovered a product called TriSalts. ( it is 3 salts: calcium carbonate, magnesium carbonate, potassium bicarbonate). Dr. Rea uses this at his clinic. As I understand it, this blocks the uptake of toxins by plugging the NMDA receptor. It can be used before OR after an exposure. It costs about $11.00 and is available at most health food stores. I find it easy to carry with me and very fast-acting. I got a mold exposure and fragrance yesterday but this worked within 30 min. of taking it. I use 1/2 tsp. to 1 tsp. in 8 oz. of water. I carry it with me in a little glass spice bottle….it keeps well and does not need to keep chilled.

    • According to Dr Rea’s book, Chemical Sensitivity Vol. 4, trisalts work because most reactions cause an acid pH and trisalts are alkalizing. Magnesium is an NMDA receptor antagonist, but not as effective as dextromethorphan. For anyone not already taking magnesium I think it would be worth trying magnesium before trying dextromethorphan, but remember I’m not a doctor and this isn’t medical advice.

  2. brainfan

    This looks very interesting and it’s very timely as I’m now facing more exposures, but they’re predictable. I’m willing to try BOTH. Thanks!

  3. I take the magnesium and tri salts. I’m about to try this brand of lozenge with dextramethorphan:

    • I hope you find it helpful!

      • Thank you

      • Misha

        It works! I went to a clinic for mamagram and ultrasound with 3 staff members FF except for the one that wore ‘Redkin natural roll on deodorant that smelled like litchen. I took 4 over a two hour period: in car, in clinic, car again. I was fine (mask and scarf on, obviously), then pushed it and went into supermarket for first time in years, apart from Costco, but I got disorientated and bought naughty food! Lol, I was on a roll, living on the wild side😷

      • That’s great!

  4. Very useful summary Catherine! I worked well with the Strepsils lozenges, now gone as you mention and I’ve just run out of me meagre stock. The only others I can find are Bisolvon, but their ingredients list is long and not conducive to good health. Are these the ones you tried, or do you know any others? I suppose we could use the syrups, though I can’t find an ingredients list for Robitussin Dry Cough Forte and they don’t publish a consumer medicine info sheet.

    • I’ve just been taking sublingual B12 which definitely helps, but I haven’t tried it with a big fragrance exposure yet.

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