Hi candiak.
I would say 300 mg Wellbutrin is causing side effects that you have mentioned. I started to get similar side effects as well. There was also concern from my doctor to be on 300 mg Wellbutrin once a day because it lower the seizure threshold. In other words, I would be more likely to suffer from seizures if I continued with 300 mg once a day.
If dose 150 mg could be in AM and then 6 hours later have 150 mg, that might decrease the side effects. It did for me. Also, be aware that I had to take it earlier than 4 pm because it made it difficult to fall asleep. Hope my experience with Wellbutrin helps you decide on what you need to do. Just remember that everyone may have different responses to medications.
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