What are the similarities of a drug and a illegal drug?

Answer 1

"Illegal" is a relative term. An illegal drug in one country can be legal in another.

A drug can be legal for someone who has a prescription, and illegal for anyone else who does not. For example, morphine in most countries is recognized as the "gold standard" to treat agonizing pain, whether from surgery or serious injuries from bullets/explosions during war. However, for anyone who does not have a doctor's prescription, possession or use of morphine is illegal.

So for many drugs, they can be both legal and illegal depending on the person using or carrying it. Having a pill like morphine for which you were not prescribed is illegal, and you face penalties almost as serious as if you were carrying heroin. The guy next to you dying of cancer with a prescription to morphine can freely walk around with it and won't be arrested if stopped by police.

Then there are some street drugs that aren't available by prescription, like heroin, cocaine or methamphetamine* because they have absolutely no recognized medical application. Therefore, they are made illegally by criminals around the world in backyards, bathtubs, or out in the forest using very dirty and questionable techniques. The purity is different every time and the cleanliness is very questionable.

Unlike prescription medications, a user can't always judge a safe dosage because the product is different every time. These street drugs are often mixed or "cut" with any and every possible substance that resembles the drug so that they end up with more product to sell, and make more money. Then it's sold to another dealer who also mixes in other crap to have more stuff to sell.

So, street drugs are dirty and usually have a whole bunch of other drugs or chemicals in it with only a fraction of it being the desired drug.

*In the U.S., methamphetamine is available by prescription in very rare circumstances and requires a ton of special approvals from medical professionals and the DEA, and therefore maybe only one in 10 million people can actually get all the paperwork/approvals, and those individuals are highly monitored.