I read all the advice given so far. The only correction I can give you is, an addict WILL LIE to you, looking directly into your eyes. You want with all your heart and soul to believe him. His addiction has taken over his heart and soul. His addiction will lie to you. His addiction will cry real tears. His addiction will promise you anything. His addiction will be so convincing. And there you are, wanting this to all go away, loving the man he was (appears to be when he has his "meds"). Nothing matters to the addiction except getting more of what it needs. Only the addict truly doesn't believe that. The addict truly thinks he has everything under control and that you are over-reacting. Using the safety of your son and your personal health needs will probably not matter to the addiction. If the addiction is in place long enough, it has control over the man you love and he doesn't care (regardless of what he tells you). The addiction will not go away just because you lock up your meds. I am so sorry to be so blunt. Addiction sucks.
Consider that perhaps losing (or walking away) from his job might be a good idea. Perhaps the pressures of this job are what prompted the the drug use. If so, there is no way he can go through withdrawals and work the rehab process while under the same pressure. If you are ready to see this through, be prepared for the financial fall out. Again, I am so sorry to sound so negative. Your husband can beat this. You can come out OK. But it won't be easy.
Rehab will probably be the answer. Expensive. Usually needs at least 3 tries. With all of the heartache in between. I am not trying to discourage you. But this is the reality of addiction. Rehab is also public, so to speak. Your family and friends will know. I have complete empathy with you wanting to keep this private.
In an effort to keep "privacy" I found a program online with a workbook. The Jude Thaddeus Home Recovery Program. Maybe this will help help lead your husband to an in-house rehab program. My adult son never even got to see it. He has been dead 3 years now. He would have been 30 on his birthday this year. His addiction was not prescribed meds, but the premise of addiction, be it tobacco, alcohol, prescribed drugs, or illicit drugs is the same.
From my research: Addiction is a brain disease. Relapse is part of the disease but not necessarily a sign of failure. Addiction is a treatable illness. The longer an addict is in treatment the greater the chances treatment will be effective. Addiction is NOT a moral failure. Drugs and alcohol can "hijack" the brain's reward system and pleasure pathways. The risk factors for addiction may include genetic and environmental factors such as stress and availability. Treatments for addiction are as effective as treatments for other chronic relapsing diseases such as diabetes, hypertension, and asthma.
I speak to groups regarding choices. I hope to be able to affect at least one life, but mostly I do it for me - so that I can feel the child's life that I gave birth to has meaning. If I had the magic words to say to your husband i would. I don't. But keep trying and trying if you have the emotional strength to. But don't forget about your son. He needs you too. Whatever your decision is, it will not be wrong. You are in a tough spot. My heart truly aches for you. I wish my son's wife was strong enough to have worked to get him the help he needed. Maybe your husband's mom feels the same. You might get support there. But I know very few people understand addiction and you might have to spend a good deal of time educating others.
Addiction is not easy to deal with but many, many people work through it. Keep educating yourself, weighing advice you are given, and keeping yourself - first and foremost - healthy. All good wishes go out to you.