Methadone is a syrup made to taken orally and definately NOT injected. Your partner is at risk of really damaging his veins (methadone will eventually cause hard lumps in his veins which in turn could clot the blood) and at worse, he could end up losing his hand, arm or a limb! I am an addict of 13 years and have used various types of drugs not made to be taken intravenously and was lucky NOT to lose my hand. Please tell him to tread carefully or even better, STOP. If he insists on continuing with this, make sure he uses butterflies as it's easier to see if you are still in the vein. Good luck to you and yours.
My Partner is an ex heroin user. He stooped using heroin before I meet him but has been using methodone for as long as I have known him. He is not prescribed Methadone but buys if off friends who are on the program and injects them instead of drinking it. He also uses it to mix with other drugs and make stronger ones similar to heroine. I realise that Methadone is used to stop heroine use buts whats the difference when he uses it like this.