The effects of heroin will vary from person to person depending on the characteristics of the:
Individual (user) – Mood, physical size, health, gender, previous experience with heroin, expectations of the drug, personality, whether the person has had food and whether other drugs have been taken.
Drug – The amount used, its purity, and whether it is injected, smoked or snorted.
Setting (environment) – Whether the person is using with friends, on his/her own, in a social setting or at home, at work or before driving.