Venlafaxine is also known and classified as a bicyclic antidepressant, meaning that the chemical structure of the drug consists of two rings.
Introduced in 1993, venlafaxine has become a popular antidepressant and is known as one of the most stimulating antidepressants available, often making it a poor choice for sufferors of anxiety; interestingly, the medication is indicated for the treatment of generalised anxiety disorders, a quirk similar to that found in the SSRI antidepressant fluoxetine. It is generally seen as an updated version of the drug nefazodone of the same class and in turn is also viewed as the precursor to the drug duloxetine, also of the same class.
Venlafaxine has proven useful as a therapy for treatment resistant patients who have failed to react favourably to other antidepressants. On top of this, the drug typically has a relatively strong antidepressant effect, another reason for the popularity it enjoys.
Unlike most antidepressants, venlafaxine often causes weight loss which is often substantial; as a result it is being assessed as a treatment for obesity, but this use is not endorsed or recommended by the current patent holder, Wyeth.
The mode of action is in this case rather novel. At low doses, only serotonin is affected (whose reuptake is blocked, increasing the amount of said monoamine neurotransmitter available to neurons at any given time). At doses of approximately 225mg per day, the drug also affects the monoamine neurotransmitter noradrenaline in the same fashion. Finally, at high doses of approximately 300mg per day and above, the monoamine neurotransmitter dopamine is also affected, again in the same fashion. As the maximum outpatient dose is 225mg a day, full therapeutic effect requires an inpatient status; moderately or lightly depressed individuals tend not to respond to dosage increases over 225mg per day.
After three days of treatment, the medication reaches a steady chemical concentration level in the bloodstream; however, full therapeutic effect is typically not experienced sooner than three weeks into therapy; a month is a sensible timeframe.
Since venlafaxine has a relatively short half life, it is advisable to take the drug in divided doses throughout the day in order to prevent peaks and troughs in mood. Extended release variants pretty much eliminate this concern.
Unfortunately, venlafaxine does have its share of downsides. Typically speaking, the medication suppresses sexual desire and increases blood pressure, the latter especially at higher doses, making extensive therapy with this drug unsuitable for patients with heart conditions or high blood pressure. As mentioned above, venlafaxine is a strong stimulant, so sufferers of anxiety may want to pass on this drug; those who are treated with it would be well advised not to take this medication late on in the day as it may very well turn you into a bit of an insomniac. Those who react badly to the stimulation may inevitably become more agitated and/or depressed, which unfortunately raises the chances of self harm or even suicide; this is noted in a black box warning attributed to the drug. Further to this, patients with poor impulse control (such as is featured in a borderline personality disorder) or a history of substance abuse should not be treated with venlafaxine.
The most common side effects include nausea (37% chance), headaches (25% chance), somnolence (23% chance), a dry mouth (22% chance), dizziness (19% chance), insomnia (18% chance), constipation (15% chance) and nervousness (13% chance).
Perhaps the biggest problem with this drug is the withdrawal process. Compared with most antidepressants, withdrawal symptoms for this drug are marked; close care must be applied during discontinuation, a process that can often take several months given the typical weekly reduction of just 37.5mg per week. Symptoms typically include agitation, headaches, nausea, fatigue, dysphoria and odd sensations often described as "brain shivers". Patients with extreme difficulties in withdrawing from the drug should be very slowly transferred to the SSRI antidepressant fluoxetine, which can in turn be discontinued at a later date with far greater ease.
