A combination of bad hygiene and depression will cause rather dramatic changes to a person. There are drug users, and then there are junkies. The media continually conflates the two because it's never very analytical about drug use. Take cocaine for example. The majority of cocaine users in the UK are in the Media and Finance sectors. i.e. most of them are successful businessmen with significant income flows, or functional drug users. 10% or so are addicts or junkies.It basically comes down to the chemistry in your body. Most of those cocaine users take a line every couple of days. It's a 'party thing' for them.Junkies cram as much drug into their body as possible. It's extreme version of what happens with food. Most of us eat more or less food in some kind of cycle, there is a balance. A considerable portion of the population loses their self control and eat as much as they possibly can. People regularly die from overeating, and they die from taking drugs. The key difference is that the quantity of a drug that can kill you is fairly small in size, less than an ounce of most drugs sold here or inside a pharmacy of any class will probably kill you stone dead no matter how pure they are. That is partly why overdoses occur. The junkie or newbie drug user doesn't work out the half-life of the drug in question, and winds up taking more than they realized over a period of time. Some drugs also distort your perception of time, so that's an issue.So that's Reason No.1. People take too much in too short a period of time. Usually this is related to being a newbie or having mental issues like depression. Obviously this is more likely with drugs that create a greater 'high', such as meth or cocaine.Reason No.2 is pharmacological. Many street drugs are not professionally produced by good laboratories. As such, a lot of drugs, MDMA in particular, have many adulterants in them. This is partly because those people haven't a fucking clue what they're doing, and partly because they pass through many hands with an incentive to 'bulk up'. In fact, a good portion of ecstasy pills, do not actually contain MDMA at all! (seriously think about getting that drug test kit).Reason No.3 is also pharmacological. Drug interactions. Most functional drug users take either milder drugs such as weed/LSD/MDMA, or they take exclusively one hard drug at a time e.g. cocaine. Junkies on the other hand, continually skip from one drug to the next, forever in search for the next high. Junkies are in denial about coming down from a high. Eating chocolate and drinking coffee makes me feel good. But I know if I continually eat chocolate and drink coffee I'm just building up a tolerance to my "drugs". The same applies to drugs, only an order of magnitude more so. If you have a variety of hard drugs in your system, even if they are of the appropriate quantity and are pure, you are much more likely to suffer from the side affects of drug interactions. (e.g. frequently turns people into miserable cows)--In my view, a responsible functional drug user of hard drugs does things like these:- Purchase a decent milligram scales to weigh quantities.- Purchase a timelock safe if the drugs you take alter perception of time.- Take one drug at a time to avoid drug interactions and know the half-life for those drugs.- Use a drug testing kits to ensure you have what you think you have.I think this is just common sense. You can acquire all of the above for less than $200tldr; You should apply the same precautions taken when you take pharmaceutical drugs, to illegal drugs, with a dollop of common sense.Conflict of Interest Disclosure: I will be selling drug testing kits on the Silk Road in the future 8)