Thank you for your question. I agree with Dr Paul Ang that Zyrtec D will likely help with your cold symptoms even though they are not due to allergies. The mechanism of Zyrtec D has been well explained by Dr Paul, and I shall only add on that a Cochrane review (a summary of the best quality scientific papers) on whether antihistamine works in cold patients showed some benefit in reducing the severity of the symptoms, compared to a cold sufferer who didn’t take it.
The “D” component of Zrytec D will quite likely help reduce nasal blockage, regardless of whether it is due to allergies or cold. Do take note that oral decongestants should not be used long term (preferably not longer than 10 days continuously) as they can cause other problems (e.g high blood pressure).
A common cold is due to a viral infection and your body usually fights it off, and you recover within 7-10 days. If your symptoms last longer than this, it is likely to be a bacterial sinus infection (bacterial sinusitis) which requires antibiotics and a nose wash in addition to the nasal steroid spray that you use. Sometimes it is difficult to differentiate a flu/cold from sensitive nose (allergic or non allergic rhinitis) or sinusitis.
To find out the difference between these, do check out the recent article on sensitive nose published on Human. Hope this helps.
