Singulair (montelukast) is a prescription medicine specially designed for the prevention of asthma attacks. You may be also prescribed this medication to deal with the symptoms of allergies, such as sneezing, runny nose and a number of other ones. Singulair is not going to treat an attack of asthma once it's in progress. This may happen if you are not using your medicine regularly, or if the dose you are prescribed is too low. If you keep getting asthma attacks and need to use some fast-acting drug every time to deal with them - talk to your health care provider about a dose increase, but do not do it yourself. The following symptoms may also indicate the dose of Singulair you have been prescribed is not working properly for you: behavior changes, thoughts about suicide, anxiety, and depression. In most cases you will get just minor side effects, such as stuffy nose, upset stomach, fever, tooth pain, cough, stomach pain, heartburn, mild rash, diarrhea, headache, and nausea. There is no need to notify your health care provider of them, as the side effects mentioned are most likely to go away on their own. Tell your doctor about any drugs you are taking at the moment (especially phenobarbital and rifampin to rule out drug interactions).