Although not approved for them, doctors may prescribe SNRIs like Effexor to treat attention deficit hyperactivity disorder, post-traumatic stress disorder, and a condition called cataplexy, which causes muscle weakness. What other drugs will affect Effexor? Taking this medicine with other drugs that make you sleepy can worsen this effect. Ask your doctor before taking Effexor with a sleeping pill, narcotic pain medicine, muscle relaxer, or medicine for anxiety, depression, or seizures. I have muscle weakness and very achy muscles esp. in the morning my feet and hands are very achy, it lasts off and on all day but in the morning its worse. fever, stiff muscles, confusion, sweating, fast or uneven heartbeats, uncontrolled muscle movements, symptoms that come on suddenly such as numbness or weakness, severe headache, and problems with vision, speech, or balance. Yes. Many specific drugs can cause weakness and unsteady gait- too many to list here. Acute and chronic alcohol ingestion may produce unsteady or ataxic gait. muscle cramps or weakness, or ; shaking. Serious side effects of Effexor XR include clinical worsening of symptoms and suicide risk, especially in younger patients. Tell your doctor if you experience worsening depression or thoughts of suicide while taking Effexor XR. Effexor XR contains venlafaxine hydrochloride in strengths of 37.5, 75, or 150 mg tablets. Effexor XR may interact with other. Summary. Muscle weakness is found among people who take Effexor xr, especially for people who are female, 50-59 old , have been taking the drug for 1 month, also take medication Lipitor, and have Pain. Along with its needed effects, venlafaxine (the active ingredient contained in Effexor) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention. Effexor withdrawal muscle pain. Common Questions and Answers about Effexor withdrawal muscle pain. effexor. How much of a factor is (was) muscle pain in your withdrawal from Effexor XR? How long did the pain last and where is (was) the pain? Any ideas why Effexor XR attacks muscle and joints? I had terrible back pain both now in withdrawal, but I also had it when I started the medicine. It. NOW it's been TEN months since coming off Effexor, and I'm STILL having major problems with muscle weakness in my arms and especially my legs. My legs constantly feel like they're going to give out on me.