Effects - Methadone as a blocker to heroin/opiates?

[beena]

SWIM has been on methadone for a month or so.....she is now on 50mls a day. Occasionally she still likes to use opiates like MST and a few times she has had a twenty bag of H (before starting the methadone programme she was taking 2 or 3 of these bags). She read that methadone can act as a blocker to opiates but thought that only happened at a much higher dose/level of methadone (say about 80mls). Is that correct? SWIM can't get any effect from taking the MST's and not much from taking heroin either. SWIM is glad the methadone has freed her from the cycle of addiction she was caught up in but would really love to take opiates occasionally still for recreational use. Is this not possible whilst she is on the methadone treatment programme? This is really pissing SWIM off! HELP!!!