Efexor XR (Australia) or Effexor XR (USA)- Venlafaxine HCl - is an extended release antidepressant of the category SNRI - serotonin-noradrenaline(USA = norepinephrine) reuptake inhibitor.
I write with personal experience of this drug for over 3 1/2 years, and personal experience with most other classes and brands of antidepressants since 1988 in the (attempted) treatment of chronic major depression.
My experience of Efexor is horrific side effects if a dose is missed.
I experience severe electric-shocks in the head, dizziness, black-outs, migraines, and emotional collapse if a dose is missed. Sometimes, if the dose is not taken right on time 24 hours apart, these side-affects will occur anyway (however, not to the same severity).
And then there is trying to get off Efexor. Ha ha. The withdrawal is so horrificly nasty that I've just stayed on it even though I know this drug is doing nothing for my depression. The withdrawal syndrome is worse than coming off opiates, and it's not just me saying it.
I stress caution in choosing this drug in treating your depression. Only try it if you are desperate and other milder drugs have failed to work.
These drugs are not supposed to be "addictive", but what they fail to tell you is that they are definitely "dependant"! Your body will become dependant on it, and there's not much tolerance for varying the time you take your daily dose due to the side-affects that seem to manifest immediately. It has something to do with the short half-life of the drug in the body. It is also worse the higher the dose.
As with all antidepressants, it is not even fully understood how these drugs work, and I would debate if they work at all, so please be careful in choosing your medication as they can have side-affects, sometimes serious. I would advise researching as much as possible using the internet. There is tonnes of information available, both lay and medical. Some of the studies I read were so wishy-washy in actually pointing to any benefits derived from this drug that it is unbelievable that they're allowed to legalise it. The extremely low percentages of benefits is appalling.
Also beware. My experience is that general practitioners (family doctors) have very little background knowledge of these drugs, and the results of their testing. They also tend to simply prescribe the ones they know, and usually don't keep up to date with the research. It is my opinion they are not suitably qualified to make a prescription. See a psychiatrist first.
Also this business of keep trying for 3 months to let it work is rubbish. Psychiatrists will tell you that you'll know within a few weeks whether or not it is working, and if not there is no benefit to continuing unless the dose is changed, or the drug is augmented with another. This is why you don't leave this process to your GP. They simply don't have the experience or knowledge to know what to do. Would you ask your dentist to operate on your brain? Yet so many people leave management of their depression to their GP because they are too embarrassed of the stigma of going to a psychiatrist. This attitude needs to be overcome first.
The action of Efexor XR is supposedly on the neurotransmitters serotonin and noradrenaline (USA = norepinephrine) in the brain. Depressed people are thought to have insufficient amounts of these chemicals in the neural synapses because they are being "re-uptaked" before they can do their job. The drug supposedly prevents this, thereby being a serotonin-noradrenaline "reuptake inhibitor" (SNRI). However, this is really only theory, as there currently is no way of actually testing the levels of these chemicals in the brain! There is no "blood test", and no way to know what is actually causing the depression.