The psychology of an addict is completely different to that of someone who is not a drug user. An addict already knows they need to quit. Confrontational behaviour such as trying to get them to ‘admit’ something, or attempting to use guilt or shame as motivators, will usually drive the person further into addiction.
Before talking to someone about their drug use, change your own perception. You need to understand what an addict feels and why they use drugs to understand exactly what you are expecting them to ‘give up’.
When you are an addict, your moral compass is non-functional, your willpower is non-existent, your emotions are stuck in the negative. Drugs are your only way to change that state. So if you want someone to stop drugs, you also have to offer them something better than drugs. Otherwise the person will quit, but then repeatedly relapse.
Remember that what you enjoy or think of as fun or rewarding, like going for a run, shopping, or even adrenalin sports, will hold no appeal for someone who has used drugs such as methamphetamine or Ice.