The war on drugs is a catastrophic failure. Every year billions of taxpayer dollars are wasted on prosecuting and imprisoning non-violent Americans. Prohibition fuels a dangerous black market where ordinary contract disputes are settled not in civil court, but in violent turf wars between gangs and cartels. Once peaceful communities have become lawless war zones; millions of lives have been ruined. Families are torn apart.
For some drugs, like meth, the production process is fraught with danger, and citizens have a right to protect themselves from lethal vapors or the threat of an exploding meth lab. The same regulations that we apply to any ultra-hazardous activity (e.g. making rocket fuel) should also apply to dangerous production facilities. As far as the sale of potentially lethal drugs (e.g. heroin, meth, cocaine, etc.), we need only look to the sale of other dangerous products for ideas on the proper scope of regulation.
For example, manufacturers of medicine are not free to sell you unreasonably dangerous drugs -- that's why there are recalls when a batch has been contaminated. Most distributors must be licensed (e.g. pharmacists), and full disclosure of all risks associated with any medicine is imperative. Sales to minors are strictly forbidden. Failure to adhere to these standards will subject the seller/producer to strict products liability in court, substantial government fines, and even criminal liability if the reckless behavior results in injury or death.
As for the users, they should have the right to ingest whatever they want provided they are over 21, don't drive or operate dangerous equipment under the influence, and do it in the privacy of their own property. At the same time, employers should have a clear right to drug test any employee; and for workers performing critical life/safety duties, (e.g. airline pilots, surgeons, and the like) rigid and mandatory drug testing should be required.
Of course, these are not the only solutions, but they can't be worse than the status quo, which is hemorrhaging cash, putting millions of non-violent people in cages, and enabling the senseless terror and violence of the black market.