Since you say you got anxious before stopping, in fact was the reason you stopped, it appears you got this side effect from taking the med. If it were from withdrawal, it would have started only upon stopping the drug. That doesn't mean it's impossible for you to be suffering withdrawals, but it would be a less likely case for that to happen given you weren't taking them every day, and you didn't take them for very long. The only way to know for certain if stopping a drug is causing withdrawal is to start taking it again and if the problems go away it's withdrawal, but again, in your case, you got the panic attack while still taking it. Now, given you had been taking it for a month before that panic attack without getting anxious, it's not clear the anxiety was caused by the medication. It might have been caused by something else entirely. Or, it could have been caused by you taking the med the way you were taking it, which would be a safe way to avoid addiction but some people get withdrawal reactions more easily than others and it's possible the brain couldn't handle the drug being there and then being taken away and did this to you. Keep in mind that this drug, while a synthetic opiate, also acts like an SNRI antidepressant, meaning it also affects serotonin and norepinephrine. Drugs that affect norepinephrine, also called noradrenaline, can cause anxiety. There's also a withdrawal from taking antidepressants for many who take them so this drug seems to give you a two-fer for withdrawal potential, but again, you didn't take it for a long time and you didn't take it every day. I would have counseled you to talk to your doc before quitting cold turkey just because of the withdrawal potential, as he might have tapered you off of it, but then again, he might not have. Which is a long way to say, dunno. Might be, but doesn't sound like it. Sounds like you either had a bad reaction to the med or you got a panic attack for some other reason.