In the UK, mephedrone and other so-called 'legal high' derivatives have recently been classified as Class B, Schedule I under the Misuse of Drugs Act 1971. Since then, alternative products have been advertised on a number of websites. In order to obtain an immediate snapshot of the situation, 24 products were purchased online from 18 UK-based websites over a period of 6 weeks following the ban in April 2010. Qualitative analyses were carried out by gas chromatography ion trap mass spectrometry using electron- and chemical ionization modes, nuclear magnetic resonance spectroscopy, and comparison with reference standards. Overall, the purchased products consisted of single cathinones or cathinone mixtures including mephedrone, butylone, 4-methyl-N-ethylcathinone, flephedrone (4-fluoromethcathinone) and MDPV (3,4-methylenedioxypyrovalerone), respectively. Benzocaine, caffeine, lidocaine, and procaine were also detected. The emphasis was placed on 'Energy 1' (NRG-1), a product advertised as a legal replacement for mephedrone-type derivatives usually claiming to contain naphyrone (naphthylpyrovalerone, O-2482). It was found that 70% of NRG-1 and NRG-2 products appeared to contain a mixture of cathinones banned in April 2010 and rebranded as 'new' legal highs, rather than legal chemicals such as naphyrone as claimed by the retailers. Only one out of 13 NRG-1 samples appeared to show analytical data consistent with naphyrone. These findings also suggest that both consumers and online sellers (unlike manufacturers and wholesalers) are, most likely unknowingly, confronted with the risk of criminalization and potential harm.