Edit: We have also detected purple and pink Heisenberg pills with pentylone in them. Avoiding this press completely is recommended.
The beige Heisenberg tablets currently available contain NO MDMA but instead contain pentylone, a synthetic cathinone stimulant.
The pills will react bright yellow with the marquis reagent, whereas MDMA goes black so these ones are easy to spot as rubbish.
Pentylone is slightly like mephedrone but lasts longer and is much less enjoyable.
Because it is less enjoyable but does have an effect, people tend to think they just have weak pills and need to take more to get the buzz they want. This results in a very high dose of pentylone, which prevents sleep for hours after it wears off, and along with its stimulant effects can cause paranoia and psychosis, as well as totally ruining your night.
Pentylone is class B in the UK.