When actors play drug addicts in movies, are they affected by the drugs they have to take?

I believe it's acting, they don't actually "take" the drugs.

When actors do drugs during a scene?
Most of the drugs are fake (Such as coke and all that) and uses special effects to make it look like the user took it. But for needles, I think it's a fake needle as well (Needle is dull and retracts into the bottle and nothing really injects, but taken out it is all okay and empty) Or it is just special effects again.

Not sure this is true but those were my thoughts.

Even the cigarettes are fake in this day and age. They are sometimes allowed a bit of alcohol for certain scenes but they do not give them drugs the same way they don't actually kill anyone, except in illegal snuff films which are so rare many people believe its myth

No but some celebrities are cannibals. They act strange when they eat other flesh for a long period of time.

It's not real cocaine.

It unlikely that they actually take the drugs while “acting”.