I am 18years and 5'8' and worried that i haven't noticed any increase in height since 6 months i have read about speed height capsules but i am scared?

Save your money: If no growth the past year, growth has stopped. Otherwise, one MIGHT grow a little more. Most people reach their maximum height in their late teens. Without nutritional problems or chronic childhood illnesses, height is largely based on genetics and parental heights. Aside from eating right, exercising, sleeping well, and being happy, there's not much a person nor his doctor can do about height.