@ysmina-- I haven't heard of any side effects and I haven't experienced any myself either. However I do know that lemongrass is diuretic, meaning it increases urine output. So you might need to drink some more water if you have lots of lemongrass tea. It might also increase the effect of diuretic medications.
Lemongrass herbal tea is so beneficial though. It has antioxidant effects and can help aid weight loss. It's also rich in vitamins and minerals. It has calcium, magnesium, iron and potassium. Some researchers say that it also has anti-bacterial and anti-fungal properties.