Helium does not kill brain cells and helium is not a drug. If helium was a drug we wouldn't be able to put them in balloons without a prescription. The bad thing is helium can kill you. Not because the gas itself but not getting enough oxygen. If you were breathing in enough oxygen and inhaling helium then there would be no harm done.
Next thing I wanted to talk about was, The heavier the gas is, the slower sound waves will travel. So your voice will sound deeper. Helium is six times lighter than air. So when you talk your sound waves are going at a higher rate making your voice sound high.
