Along with its needed effects, montelukast (the active ingredient contained in Singulair) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention. In 36 posts found by Treato discussing Singulair and Loss of Appetite, no patients reported Singulair causing Loss of Appetite. The manufacturer's product labeling should always be consulted for a list of side effects most frequently appearing in patients during clinical studies. Side Effects. Drug information provided by: IBM Micromedex. Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention. Increased appetite is found among people who take Singulair, especially for people who are female, 60+ old , have been taking the drug for 1 month, also take medication Xyrem, and have Narcolepsy. This study is created by eHealthMe based on reports of 77,028 people who have side effects when taking Singulair from FDA, and is updated regularly. The most common side effects with Singulair include stomach pain, stomach or intestinal upset, heartburn, tiredness, fever, stuffy nose, cough, flu, upper respiratory infection, dizziness. Singulair Side Effects Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention. Increased Appetite Side Effect Tricyclic antidepressants (imipramine, amitriptyline, and doxepin) cause carbohydrate craving and increased appetite 1. First-generation antihistamines, most antipsychotics and systemic corticosteroids also may cause increased appetite. i abruptly stopped my son's singulair after i realized the side effects he was suffering. it took a full 2 weeks to be.he was like a different child after taking singulair for 3 years. as for him, he did not suffer any.the only thing i noticed was an increased appetite. i do believe that this was caused by him feeling so much. Toggle Singulair Side Effects - Medications.com Actual Singulair side effects submitted by users. Singulair is a leukotriene facial tic, poor appetite , I did not recognize that he was suffering side effects until his ped increased his dosage to 5mg. “ Side Effects: Increased appetite I love Singulair-- for me it's a wonder drug. When I'm on Singulair I can breathe freely, my skin doesn't itch, and I can even go outside without sneezing. When I'm on Singulair I can breathe freely, my skin doesn't itch, and I can even go outside without sneezing..