The terms "soft drugs" and "hard drugs" are arbitrary terms, with little to no clear criteria or scientific basis.
Typically, the term "hard drug" has been used to categorize drugs that are addictive and injectable, notably, heroin, cocaine, and crystal meth. Marijuana is usually the only drug included within the category of "soft" drugs, although some people include nicotine and alcohol in the soft drug category because of their legal status for use by adults, and their relative social acceptability compared to illegal drugs. The term "soft drug" is sometimes used interchangably with the term gateway drug, a term that is equally inaccurate.
Use of the terms "hard" and "soft" drugs raises more questions than it answers. Is a drug only "hard" when it is injected? Surely heroin, crack and meth are not "soft" drugs when they are smoked. With these drugs, it is the purity, amount, frequency of use, social context, and route of administration that typically determines how harmful it is.
And the implication that marijuana is a soft or relatively harmless drug is being increasingly questioned. There are several different types of marijuana, with hashish and hash oil traditionally being thought of as harder forms of cannabis. However, stronger strains of weed are being genetically engineered and longer-term harms are becoming more apparent.
Criminological research shows that few drug offenders limit themselves to only one drug, bringing into question the idea that drug users are able to limit themselves to a single "soft" drug, although there is a clear pattern among this population of progression from marijuana to heroin.
If we were to categorize drugs according to how hard or soft they are, several drugs would be particularly difficult to categorize. Hallucinogens, such as magic mushrooms and LSD, and the rave drug ecstasy, are generally not considered by users to be addictive -- although some research tells a different story. But given the lower incidence of addiction to these drugs, and the fact that they are taken orally rather than injected, would they be considered soft drugs? As the risks associated with bad trips and flashbacks are well-documented, and with their status as controlled drugs, it is unlikely that experts would support the view that they are soft drugs.
And which category would prescription medications, such as tranquilizers and painkillers, go into? We don't usually hear the term "hard drugs" applied to these medications, even when they are abused, yet some are chemically similar to heroin, while others are among the most addictive drugs around, and the most dangerous to withdraw from. So the soft drug category doesn't fit for them, either.
So the terms "hard drugs" and "soft drugs" don't tell you much about the drugs being referred to. They are used mostly for dramatic effect, to get across the speaker's perceptions about the relative harmfulness of one drug compared to another. So your drinking buddies' encouragement of marijuana use is simply peer pressure, and calling weed a "soft drug" doesn't mean it is harmless.
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