Not true in general, and certainly not true in specific cases. There are over 16,000 drugs used by humans, and very few of them are hazardous at the correct dose. Are they hazardous at incorrect dosage? Some are, some are not, but then almost anything, water included, will kill you at inappropriate dosage. Many illegal recreational drugs such as LSD, psilocybin and DMT have no known lethal dose.

they contribute to a black market and all the related crimes of drug trafficking

That's simply a function of them being illegal. If they were not illegal, they would not "contribute to a black market and all the related crimes of drug trafficking".