the strength of a dose is affected by your weight

scientifically and in medicine dosages are given or chosen using mg/kg (eg 10 mg/kg of bodyweight should have a similar effect in most people). this is because the drug distributes throughout all or most tissues, then is slowly released depending on how strongly it binds to those tissues, therefore determining the half life. and because of this only a small amount of the drug ingested is bound to stuff in your brain. less fat and muscle means more in your brain and vice versa. half life's can be variable though in different people and drugs are metabolised in all different ways so it's not perfect to predict. I always look at graphs like this to guess how I'll feel but maybe I'm just a nerd. you can usually find them by searching (drug name) blood concentration graph since scientists always study this stuff before a drug is made available

drugs such as methylphenidate that naturally have small half lives are slowly released using a capsule that is digested at different rates. concerta looks like this . vyvanse is much smoother since it naturally has a long half life

half life's are the same for most doses for most drugs but there are outliers depending on how exactly the drug is metabolized.

hopefully this was way more than you asked for but this is what vyvanse does to me lol

basically heavy people are less sensitive, light people are more sensitive. and everybody has small to large variabilities in how their bodies metabolise certain things and especially how their brain feels on that drug