I'm 18 and I have adhd. How do I control my impulsivity?

See a psychiatrist. For treatment of your add and she can also work with you on your impulsivity.
Low sugar, low carb . Adhd attention deficit hyperactivity disorder is often caused or worsened by fluctuating blood sugars as a result of sweet drinks. Reactive hypoglycemia leads to inability to concentrate as the brain is temporarily starved for glucose. Then the low sugar levels stimulate the release of adrenaline leading to the hyperactivity.