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People use over the counter (OTC) medications to relieve symptoms of the common cold.
However, these symptoms are part of the immune response, right? They are driven by the body responding to the virus and attempting to make the body less habitable and thus easier to kill it off.
Do OTC medications that reduce cold symptoms cause the cold to persist longer? Should such medications be avoided if the goal is to reduce cold duration rather than symptoms?
It is plausible but by no means established that antipyretics (fever suppressors) in particular could increase the duration of infection/symptoms, because fever is part of a functional immune response.
From Graham et al 1990 (a small [n=56] randomized trial of the use of antipyretic pain relievers in volunteers experimentally infected with rhinovirus):
Use of aspirin and acetaminophen was associated with suppression of serum neutralizing antibody response (P less than .05 vs. placebo) and increased nasal symptoms and signs (P less than .05 vs. placebo) ... There were no significant differences in viral shedding among the four groups, but a trend toward longer duration of virus shedding was observed in the aspirin and acetaminophen groups.
In other words, it looked like the people who took aspirin or acetaminophen had weaker immune responses and more cold symptoms. They might have been infectious for slightly longer, but it's hard to tell (also, duration of infectiousness is not the same as the duration of symptoms ...)
However, a review (Kim et al 2013) concluded that NSAIDs (non-steroidal anti-inflammatory drugs) slightly (but non-significantly) reduced the duration of illness.
In a pooled analysis, NSAIDs did not significantly reduce the total symptom score (SMD -0.40, 95% CI -1.03 to 0.24, three studies, random-effects model), or duration of colds ([mean difference] -0.23 [days], 95% CI -1.75 to 1.29, two studies, random-effects model) [emphasis added]
Here is the figure from that analysis:
"Common cold" is often considered synonymous with rhinovirus infection, but may also include mild influenza infections. An observational study on influenza A and two other infections (Graham et al 2000) found
There was a striking correlation between antipyretic therapy and duration of illness in subjects infected with influenza A and S. sonnei, but not R. rickettsii ... Multivariate analysis suggested that antipyretic therapy prolonged illness in subjects infected with influenza A, but its use was the result of prolonged illness in those infected with S. sonnei.
In other words, to the extent that one can really distinguish causality in an observational study, it seemed that taking antipyretics made influenza illness longer, but that causality went in the other direction for S. sonnei (i.e., people took more antipyretics when they were sick for longer).
The usual caveats associated with small studies and researcher degrees of freedom apply when interpreting the results of these studies ...
The common cold as a clinical syndrome is not any particular viral infection, but a cluster of symptoms that follow a stereotypical course. It's generally associated with an initial viral infection and you can isolate infectious particles early in the course of the illness, but by the time most people go to the doctor there is no active infection. Because of this, care for a common cold is directed at the symptoms. You could even say (and I do) that the common cold is the symptoms, not the infection.
The development and resolution of many common cold symptoms are unrelated to direct infection. Cough, for example, when associated with the common cold, is not due to infection directly, but reactive inflammation, and is one of the symptoms that lingers the longest. Treatment limiting postnasal drip and, in patients with reactive airway disease, any associated asthma flare up can shorten the length of the illness.
So, no, treating the symptoms in the case of the common cold is not a bad idea, and does not cause the disease to last longer. It may even shorten the disease course.
You can see some of these principles discussed in these clinical practice guidelines and in this review of the pathogenesis of one of the viruses most often associated with the common cold syndrome.
The general principles in this answer are discussed in Cecil Medicine Ch. 369 and Bennett Prinicples and Practice of Infectious Disease Ch 58. If you're interested in the common cold, I highly recommend reading both of these chapters. Though they were from now dated earlier editions, these chapters really helped me get a grasp on how to approach clinical syndromes in infectious disease when I was starting out.
See the comments below for valid criticisms of this answer. While the common cold is simple in many ways, good evidence on this syndrome is not simple or common. Host -pathogen interactions are variable at best, and there are thousands of viral serotypes that cause the common cold (many of which cause other illnesses too). My answer here is a synthesis of treatment recommendations and a clinical approach. As @anongoodnurse says, this is probably not a good way to answer a layperson rather than a serious student of human biology via clinical medicine. The summary is pretty simple. If you use medicine that is safe to make someone with a cold feel better, you've taken care of that person's cold. If you don't have the access or background knowledge to digest Cecil and Bennett, believing this requires you to take an anonymous internet typist's word for it. Because of that, it may not be a good SE answer.
