A weakened immune system can result from environmental factors, stress, an unbalanced diet, lack of exercise, little sunlight and certain medications such as antibiotics. An immune system boosting therapy can help to strengthen the immune system, especially if you feel listless, have frequent colds or have had to take antibiotics for a long time. A therapy aims to rebuild the immune system over several weeks and start a healthier lifestyle. It is best to go when you are not actively sick with a cold or similar.