Even more critical is to know the potential side effects if you are on an MAOI.
I only took a single teaspoon of Delsym. Obviously, your combination of medications and/or biology tolerates the combo.

Some important background which has been discussed on this forum in the past:

Neuroinflammation resulting in the death or injury of critical neuronal populations is currently thought to be a key process involved in the development of several neurodegenerative diseases, including Parkinsons disease.

Dextromethorphan (DXM) is one of a class of closely related drugs called morphinans which includes naltrexone and naloxone. One these, naltrexone, has been used for several years at very low doses to ameliorate symptoms of several diseases such as multiple sclerosis These three drugs were shown by the research group of Dr. J-S Hong in 2005 to inhibit the inflammatory activation of microglial cells in mouse brain slice cell tissue culture which included dopamine-secreting neurons of the type lost in humans in the course of Parkinson's disease. Importantly, this inhibition was observed with these drugs present at extremely low concentrations, but not at higher concentrations.

Delsym is a formulation of DXM which not only contains the drug at the higher concentration, but also includes polystyril, a substance which causes the DXM to be slowly released.

In 2006, in a discussion with Dr. Hong in which I revealed that I was using low-dose DXM
to treat my PD, he cautioned me to avoid DXM preparations containing other additives, especially those that could affect the rate of release of the drug. It seems to be important that these drugs be present as a "spike", at a low concentration for a short time span in order to achieve suppression of microglial cell inflammatory activation.