The common cold is more common than you might think. The average adult will usually have two to five bouts with the common cold a year while children may have six to eight common cold episodes a year (Simasek, 2007). The medicine prescribed by doctors or recommended tends to be “harmless” OTC medications; products like Nyquil, Robotussin, with the main ingredient being dextromorphan (DXM). This product is relatively harmless and will treat symptoms of the common cold for most, but for those that are CYP-2D6 deficient, DXM could spell trouble, as in psychotic trouble.
DXM, when taken in excess, can produce euphoria, dissociation from the mind, psychosis, feelings of omnipotence, panic attacks, hallucinations, etc. This comes from personal experiences, albeit unintentional. I took about two times the standard dose of Robotussin to alleviate my unrelenting coughing fit two years ago. With it, I started to feel drunk-like and experienced a feeling of euphoria, stimulation, social inhibition, and weird body sensations. The abnormality of this was that it persisted for about two days. This leads me to believe I have very little CYP-2D6.
For some background information, CYP-2D6 is a gene that is responsible for the breakdown of pharmaceuticals such as tricyclic antidepressants, antiarrhythmics, and adrenoceptor antagonists (“Genetics Home Reference”, 2016). The NMDA antagonist, DXM, is also metabolized by CYP-2D6 (Yu, 2001). A lack of this enzyme makes the physical, as well as psychoactive effects, last for much longer than is intended. If an adult or child takes the standard dose of DXM three times in that day being deficient in CYP-2D6, they could experience a “high” from DXM that could last for 24-72 hours or longer. This is because the DXM is not able to be metabolized and taken out of the body for that period of time.
I am not alone in this deficiently. Studies suggest that 7% of the population are CYP-2D6 deficient. 25% of all prescription drugs are acted on by CYP-2D6. CYP-2D6 deficiently can result in prolonged adverse effects in these medications, most notably Prozac, Claritin, Allegra, and Vicodin, and this deficiency can also activate the analgesic activity of certain opioids like codeine (Genelex, 2014). Based on this research, it is important to be tested for CYP-2D6 deficiency if one experiences effects from these drugs that last longer than it is intended.