The generically labeled medication guaifenesin is marketed under a variety of brand names in the United States that include Allfen, Robitussin, Mucinex and others. The medicine, the Mayo Clinic states, may be used in dosages sold over the counter or in higher-strength doses prescribed by your physician. Guaifenesin helps to induce expulsion of phlegm or mucus from your lungs and airways. It functions by making the mucus thinner inside your lungs. There are no reported serious common side effects of the drug.
Nausea
While guaifenesin may cause other side effects when combined with other medications, it does not produce many by itself. One of the most common non-serious side effects of taking guaifenesin as a liquid or capsule is nausea. This is a general feeling of having an upset and queasy stomach. The condition generally will be mild with guaifenesin, but it can be uncomfortable. Nausea may make it difficult to eat food or drink even water because it makes you feel as if you may throw up. Another common non-serious side effect of taking guaifenesin is vomiting. Both of these problems are reported by Drugs.com to be temporary, meaning they will continue for a few days—if you get them at all—but then go away on their own. They generally do not need attention from your physician. However, if you consider the problems severe, explain them to your doctor. Tell her, also, if they persist.
Dizziness
Guaifenesin in the liquid or elixir form may cause you to experience vertigo, commonly known as dizziness. You may think you are whirling around or spinning. You may think the rest of your environment is whirling or spinning. It may seem like everything is in motion constantly. This can make you feel nauseous. Dizziness, too, can make you vomit. It can make you feel like you are out of balance and unsteady. This may make it difficult to navigate when you are walking and moving. Again, these are temporary side effects that are categorized as non-serious. Talk with your physician if they do not end in a week.
Drowsiness
As with many drugs, even over-the-counter medicines, guaifenesin can make you feel sleepy. You may have gotten a good night’s sleep, then take guaifenesin and you may feel drowsy again. This effect should not continue long, maybe several days or a week, before ending.
