Methadone vs heroin side effects

Hi, I'm hoping 1 or 2 of you out there might b able to help me out a little. Just a little friendly advice needed please.

My partner is on a methadone program, but is prone to the occasional relapse back to heroin for short periods of time ever so often.

My question is, is there any way of knowing the difference between the side effects of heroin and methadone compared to eachother (I'm not that experienced with hard drugs, and I'm assuming all opiate side effects are similar). Making it hard to disguingish one from another?

Would be really helpful for me to know so I can pick up on things earlier to help him if there is a next lapse.

Any advice or comments will be appreciated.

I doubt that you'd be able to tell the difference between your partner on heroin vs. them on methadone.