I’ve done it. It’s acting on different parts of your body, so I don’t think you’re in any danger. A quick google search for contraindications didn’t give me anything.
Here’s the deal. Save the opiates. The psych is going to dominate your drug experience. The opiate will be the last thing on your mind. You won’t feel it, care about it, or think about it. You’re just gonna trip balls off of your psychadelic.
The opiate later, coming down from your trip, now that sounds like a good idea to me.