A few mouthfuls can kill an adolescent.
Less than 50mg can kill a non-tolerant adult (and that could include you!! - see below).
Tranquillisers and/or alcohol with methadone kill more people each year than heroin overdose!
Most of the people who die from methadone overdose have been sold it by someone who has got a script.
As you reduce the amount of methadone you take, your tolerance will reduce too. So if you do use on top of a low dose, or go back to heroin after a break, you could easily overdose on the amount you used to take.
If you ever suspect someone has overdosed on methadone, lie them on their side in the recovery position and call an ambulance - an injection can be given to reverse the effects, provided a paramedic or doctor gets there in time.