On several occasions, I know I took my effexor in the morning, but by evening, I am suffering symptoms of withdrawal (dizziness, anxiety attacks) becoming more severe throughout the night. I usually feel better a couple hours after taking my next dose in the morning. This has now happened to me about 6 or 7 times over the past year. I am now suspicious that I occasionally take a capsule that is ineffective. This has happened over the course of several refills, so I don't think it is just one bad batch. Could this be an issue with quality control if the manufacturer?