It is not possible to describe the effects of each RC. According to their categories, they have empathogenic effects (Substance inducing a feeling of empathy with others), Psychedelic (hallucinations and inner search), stimulants, tranquilizers … barbiturates (etaqualone) or synthetic cannabinoids (AM2201 UR-144 …). The whole panoply of “old” equivalents in RC. The RC may have (approximately) the effects of MDMA (5-APB .. MDAI), LSD (5-Meo-Dalt, 2-CB), amphetamines (2-AI, ethylphenidate, camfetamine, AMT) of the ketamine (N-ethyl-ketamine methoxetamine), methamphetamine (Methiopropamine) can be opiates (AH-7921, deoxy-tramadol …), benzodiazepines (etizolam) …
Unlike such as heroin, cocaine or alcohol, I do not know the medium and long term effects of research chemicals. The hypocrisy of the “Not for human consumption” and the constant renewal of molecules that nobody has the time to really experiment or research on these products and the risk reduction associations do not have the time to share a clear and independent information.
Little by little the studies are made well after the first use and learn than in England, for example, with 51% of mephedrone mephedrone users would have suffered headaches, 43% of heart palpitations, nausea 27% high and 15% had frozen fingers look blue.  with methylone or “M1” (very toxic to the brain) many trip report report feelings of ants in the persistent crane or profound mental confusion after the trip, see amnesia, requiring hospitalization.
The other main danger of RC is that they are not controlled. When you order a RC on the internet, you never really know what you will receive, or the percentage of active product or the impurities contained in those substances due to incorrect synthesis (eg MPTP in desmethylprodine), or even if this is the right molecule. Buy research chemicals
Many of the RC are made hastily in laboratories in China who are not fussy. The story of the death of a Danish seller in October 2009 is revealing in this respect.  In late September, Dannie Haupt, a seller of RC receives a cargo of what he thinks of 2-CB-Fly from its Chinese supplier. Without analyzing the product, Dannie Haupt decides to 18mg, and died a few hours later of respiratory depression. But during that time, he sells more doses to these clients worldwide. Another death in the US and several hospitalizations are put on hold. An analysis of the substance a few weeks later shows that the cargo Dannie Haupt is not 2-CB-Fly, but the bromo-dragonfly, the active dose is in the order of micro-gram. Dannie Haupt made a fatal overdose. You need to find the good RC chemicals
Like MDMA, much of RC can induce a “serotoninergic syndrome” (potentially fatal disorder of the chemical balance of the central nervous system due to an excess of serotonin in the brain.) Which can be fatal in overdose some of these molecules and / or mixtures with other or foods.