I do not think it is beneficial to use them together. Both of them are powerful drugs and they could be very hard on your system and this is due not only because of their side-effects.

The use of non-prescribed methadone without medical supervision can lead to high risks, especially when it is used as a substitute for heroin in order to get a 'high' instead of to prevent withdrawal symptoms.

Please consult a physician before using any drug, including clenbuterol!