A half-life refers to the time spent coming down from a drug. What does this have to do Gordan Freeman and Aliens?

Half life is the term used to explain the life of any radioactive material.  There are many radioactive or volatile substance references throughout the game.

" A half-life refers to the time spent coming down from a drug. What des this half to do Gordan Freeman and Aliens? "

Kyreo is right, the "half-life" is the time it takes for any substance to decay and reduce amount/quantity by half. It was most popularly used (Before the game series), to refer to radioactive decay, but is an acceptable term for anything that has a set-rate decay.
 
The more you know!

"Half-life" is a scientific term, referring to the amount of time it takes for something to decay into half of what it originally was. Blue Shift, Opposing Force, and Decay are all also scientific terms that fit within the theme of the game. It has nothing to do with drugs.

" @MeetThePyro said:

" A half-life refers to the time spent coming down from a drug. What des this half to do Gordan Freeman and Aliens? "

lmao. At least try to act smart. "

My best guess is that with Gordon Freeman being a scientist and the story of the game revolving around a botched science experiment then perhaps Vale just looked for some form of scientific term or phrase that felt right for their product.

Also, the Half Life logo - the Greek letter Lambda - is used to denote the 'decay constant' when doing hard science about exponential decay (ie. the larger the decay constant, the shorter the half life).

Its because the dude Half-Life ( Gordin Freedmen ) has half of his life as health and the other half as his suit armor. 
The suit armor is recharged from walls that use a gas pump to fill up his suit.

I suspect the OP was being sarcastic.  It has been adopted by middle class drug dealers though, heard that before.

It's all science and stuff i believe. As the above people have mentioned :)