Under prohibition, drugs like heroin and cocaine are often called "controlled substances."  That's a terrible misnomer.  Prohibition can never eliminate drug use or the drug trade.  Never has and never will.  Instead, it drives the drug trade underground into black market channels over which no legal authority can exert any control whatsoever.  Society demands that drugs be controlled, but prohibition causes the exact opposite.  
Is it something in our culture that fosters this idea that drug legalization would automatically mean a completely unregulated drug trade?  Why should drug legalization mean television ads promoting crack cocaine sales at the 7-11?  It's absurd because it's such an obviously bad idea.  But it should be just as obvious that legalization of drugs will never come about like that.  And it should be obvious, if we look at it carefully, that some form of regulated legalization is really the only way can ever regain control over these so-called "controlled substances."  
"How do you envision legalization working? How would the product be distributed? Could anyone sell them? Would you place restrictions related to age? What about driving under the influence, or using drugs on the job where performance affects others?"
There are any number of ways it could be done.  And it wouldn't have to be done the same way in every place, or even the same way for every drug.  Product could be distributed through mail order, pharmacies, specially licensed stores, liquor stores, government run monopoly stores or special clinics - just to name a few ideas.  But this is part of the beauty of legalization - unlike with the black market of prohibition, communities would actually have the power to decide how drugs are sold and by who.  
Laws against driving or operating dangerous equipment under the influence of impairment causing drugs would remain.  Who would change them?  If anything such laws would probably become easier to enforce.    
"What about those that "spike" the punch at a prom? Would this be a crime?"
Isn't that a crime now?  Drugging people without their knowledge is a crime.  And getting underage people high or drunk even with their knowledge is a crime throughout the United States.  I don't see why legalization would change this.  In a country so generally repressive toward its own youth as the United States, I'd have a hard time imagining drugs being legalized without some form of age restriction.  
"What about health issues related to the use of drugs. Should the state pick up these expenses?"
What about the health issues related to fast food and obesity?  Should the state pick up those costs?  I'm strongly in favor of a national health care system that provides free health care for everybody regardless of what may have caused their illness.  In the US, giving everybody full medicaid and scrapping the private insurance system makes perfect sense to me.  But I understand a lot of people wont agree, so I'll suggest this:
Tax drugs and you could raise huge sums of money.  This money would not only cover drug related medical bills but could also fully fund voluntary treatment programs so addicts who make the decision to enter a program can do so immediately - instead of having to wait several weeks or months as the current system usually requires.  
"Would you place measures related to concentration on the products to make it more difficult for someone to kill themselves?"
Sure.  For example, with heroin, merely assuring addicts an uncontaminated product at consistent strength would prevent many accidental overdose deaths.  
Don, may I turn this question around?  If drugs were to be legalized this year whether you liked it or not; what kind of regulations would you like to see?