hello there and thanks for writing to HCM i have read your query and understand your concern is regarding ashwagandha. Ashwagandha also known as indian ginseng which is a powerful natural herb product and has been well detailed in our ages old ayurveda. It is mainly meant for increasing vitality,energy,for healthy metabolism,better immunity and promoting quality of sleep and reducing stress. from the various documentations i have read regarding the same,thyroid disorders and pregnancy are the situations where ashwagandha should be avoided.Otherwise there are nearly no side effects 400mg that you are taking is well within the normal dosage range allowed. If you are exercising for the first time,start light and slow and understand it is normal to feel mild breathlessness and elevated pulse rate because of the increased oxygen demand experienced by the body. If its persitently causing discomfort even after 2 or 3 weeks,and you experience giddiness or chest pain etc,then visit a cardiologist who will advise you a TMT,stress test,echo and ekg and lab investigations if needed. Mentioning of your age,medical and drug history would have been more helpful. As of now,you can continue exercising lightly till you get adapted,continue ashwagandha in the moderate dose,have a healthy diet and plenty of fluids. Please stop using ashwagandha when you take other drugs and also do a liver function test and renal function test after 3months and then followed every 6 months or 1 year.. Hope i have clarified and hope it helps.follow up if further advise needed. Good day and take care