A rush is an amazing feeling that various drug classes can get you to, such as opioids and stimulants. The strength of a drug rush is determined by the speed of introduction of the drug into the body, and most importantly into the brain.It's basically the intensity of the onset.
The speed for introduction depends on the route of administration which you use. Often, the fastest methods, and therefore the most likely to get you the best rush out of your drug, are as follows in descending order:
It is important to note that not all drugs are ideal for injection or for the other ROAs; these are the fastest-onsetting methods for use with an ideal drug that is perfect for all of them. One should research any drug they plan to put into their body. Additionally, many classes of drugs do not produce any kind of rush at all; for instance, benzodiazepines aren't known for producing a rush. Finally, oral administration almost never produces a rush.
 Words of caution
The rush plays an important part in the play of drug users' lives, often a sad one. It contributes to psychological dependence, occasionally corrupting users on their first I.V. use. This can eventually lead to a crippling physical dependence, constituting a full-blown addiction to a drug. This is what you want to avoid! With meth amphetamine, do not redose for days straight! With opiates, benzodiazepines, tobacco, and alcohol, do not use every day unless you want an addiction on your hands!
If managed properly, the rush can be a very satisfying addition to your high, and users can get the most out of their drug with efficient, safely-managed ROAs which are very enjoyable. One should take it slow, and he will be fine.