Hey man, I'd like to welcome you to the forums. Nobody expects you to know everything from day one, but from day one, you definitely need to familiarize yourself with our guidelines and the overarching, esoteric philosophy of the community, which admittedly, due to the subjective nature of what we do, is constantly evolving in minute ways.
So, with that being said, we really don't like threads that are dedicated to nothing more but increasing the quality or duration of a buzz/high/intoxication. Again, I don't expect you to know this.
Being that you're a new member and you seem to be fairly new to Opioids, you kind of override this principle.
What you definitely need to avoid as a new user of Opioids:
Benzodiazepines: Alprazolam (Xanax), Clonazepam (Klonopin, Rivotril), Lorazepam (Ativan) to name the big 3 commonly found in the United States. There are of course others, so do your research before taking any pill.
Alcohol: Pretty self-explanatory. Using either of these is extremely dangerous, especially for a green user.
Barbiturates: If you encounter Barbiturates in your travels, be sure to tell me. Phenobarbital (Luminal) is the only Barbiturate you'll find in the states. Secobarbital (Seconal) and even, I think, Pentobarbital (Nembutal) are in theory, prescribable, but it's just highly, highly unlikely. If you combine Barbiturates of any kind with Opioids, as a new user, you're likelihood for death by misadventure really picks up steam.
Things you probably can take without incident
Sedative Antihistamines: Diphenhydramine (Benadryl, others), Promethazine (Phenergan), Hydroxyzine (Vistaril). These can increase the sedative effects of antihistamines in a pleasant way and its not an uncommon combination.
Cannabis: Whatever this means to you in our current climate of liberalization.
Dextromethorphan: Some people enjoy this combination and some don't. You're more likely to have a negative experience with DXM than antihistamines though.