This feels very click-baity. As far as I can tell, the assisted suicide law is being extended to include people in unbearable pain from mental health problems, not just physical ones. Because substance abuse is classified as a mental health problem, people with drug addictions would have the right to request assisted suicide under this extension to the law.
The objections being raised speak to the same fears many disabled people have about legalising assisted suicide: that people struggling with their health might be, or feel, pressured to end it for the convenience of others, not because it is the best thing for themselves. I assume that the existing law attempts to address this properly, with safeguards against external pressures.
Assisted suicide is most valuable for people who do not have the physical capacity to do it themselves, and do not want to put a loved one at risk of a murder charge. In practice, most people with a serious drug problem can quite easily end it themselves if they want to. Access to assisted suicide doesn’t seem particularly likely to change much, except perhaps offer a more peaceful, dignified death for those who want it anyway.