Tulasi or Holy Basil is a very important sacred plant for us in India (specially Hindus). Almost every house will have a plant. Tulasi plant is also used while we offer some food for god as nyvedya. Well as per for the health it is auspicious. Recently when I felt Ishaan has caught cold, I boiled tulasi leaf (3-4 leaves) in drinking water. Left it to boil for sometime. Later tried to squeeze the leaves. It let its medicine to the water. The water changed to green. Then I fed him this water once it was warm. It made him feel better and the cold was not increased. It made his breathing easy. Its very good for us too. Later I have given this medicine water for my husband and I had too. We have not caught cold from then.
Hope this medicine helps you as well.