I was wondering if you injected an alchol (drinking) straight into blood stream would it have effect?

It would get you drunk, but it could also get you dead. When you drink alcohol, your body has several defense mechanisms to keep from harming yourself too terribly much. That is to say, the alcohol is absorbed by your gastrointestinal system - it is then taken to the liver where it is detoxified somewhat so that lower levels actually reach your brain. If you inject alcohol, it would largely bypass detoxification by the liver and could go straight to your brain in dangerously high doses. If you didn't kill yourself directly by the alcohol causing you to stop breathing, you could very well cause extensive brain damage.

If you need a reminder of the harm that this could cause, give yourself a little papercut and then dunk your hand in rubbing alcohol.

would not inject drinking alchohol as it is not sterile and will likely cause infection as well as drunkeness. Also direct injection can cause sudden death, as alchohol that has been injested is absorbed slowly, and alchohol that is injected hits immediately. Less that one ounce of injected alchohol can cause cardiac arrest, or alchohol poisoning.

Obviously - why do they then take blood samples after car crashes etc - to determine the level of alcohol.......

It would probably kill you.

yes...faster too