The drug that is called "bubble" (at least in parts of the UK) is properly known as mephedrone. It is a drug that was quite popular for a while because it was not covered by anti-drug laws. This drug was being sold openly online as a plant fertilizer. It was made illegal in many European countries starting in the early 2000s. England, for example, banned it in 2010.
The drug has been responsible for a number of deaths, which is a major reason why it has been made illegal in many countries. Its legal status in the United States is somewhat inconsistent as it is still legal to sell it (as bath salts) in some parts of the US.