Though they may have different levels of severity, pretty much all illegal drugs reached their prohibited status because they were believed to be a danger to those who used them. Even so, people still seek out and use those drugs - and sometimes they might not be aware of the risks when doing so.
One of the most dangerous substances on the market at the moment is krokodil, a so-called "budget" version of heroin that - if administered incorrectly - causes the user's flesh to necrotise and rot. In fact, it takes its name from the scaly appearance it gives to the skin of krokodil addicts, as it often ends up resembling that of a crocodile's.

After a rise in cases seen outside of Russia and Ukraine (where the drug originates), experts are working to educate people on the effects and dangers of krokodil, which also goes by the names "Russian Magic", "Poor Man's Heroin", and "Zombie drug".
"According to reports, the drug is fast-acting within two to three minutes and 10 to 15 times more potent than morphine, and three times as toxic," says drugs.com. "In fact, when the toxic chemicals are removed, quite often what is left is desomorphine, a compound very similar to heroin."
Unlike heroin and other drugs of the same potency, however, krokodil is at high risk of becoming widely accessible because it is relatively cheap to score a hit. One dose of the drug can cost as little as £5 (around $6.40), as it is made from low-cost ingredients such as codeine, iodine, lighter fluid, paint thinner, industrial cleaning oil, gasoline, and alcohol.

Dr. Allan Harris, a specialist in treating drug addicts and the homeless, spoke to HuffPost back in 2013 about some early cases of krokodil use that he had witnessed in the UK. Describing one patient, the doctor said:
"He had a huge crater in his arm, where you could actually see the tendons and bone moving at the base. He was never able to use his right arm again – the muscles never grew back because they were completely gangrenous. He died this year."
And, like heroin, the substance is incredibly hard to quit.
According to drugs.com:
"Addiction is an obvious problem with krokodil use due to its high opioid potency and short duration of effect. Frequent administration may lead to binge patterns that can last for days. Users are at increased risk for exhaustion due to sleep deprivation, memory loss, and problems with speech. Variations in potency or "homemade" recipes can put users at increased risk of overdose."

The effects of krokodil are debilitating, and even a single use of the drug can cause irreparable harm. Past users have reported external symptoms such as open ulcers, gangrene, and rotting gums, internal complications such as organ damage, bone infections, and blood poisoning, and cognitive issues such as memory loss, impaired motor skills, and difficulty speaking.
Krokodil users can overcome their addiction with help. If they do not, however, they are reportedly likely to die within two years of first starting to take it. Therefore, the more awareness that's raised about this, the better.