Different Types of Antidepressants
SNRI, SSRI, MAOI, TCAs and other Drugs Used In Depression
Jan 27, 2009
Clinical depression is a chronic condition that can be treated with psychotherapy and other non-drug therapies, but often medication can be a very helpful addition and there are many types of antidepressants. Some people get a good match on the first try, others have to try multiple ones to find one that helps.
SSRIs
Selective serotonin reuptake inhibitors are the most commonly used group of antidepressants, which includes e.g. fluoxetine (Prozac), sertraline (Zoloft) and citalopram (Celexa). They increase the levels of serotonin in the brain.
It usually takes several weeks with the SSRIs until the effects are noticeable. Nausea, insomnia, drowsiness, and sexual dysfunction are common side effects. Weight gain is possible.
SNRIs
The SNRIs include venlafaxine (Effexor), desvenlafaxine (Pristiq), duloxetine (Cymbalta) and milnacipran (Savella, Ixel). Besides serotonin they also increase brain levels of norepinephrine (noradrenaline). This is often useful in the treatment of chronic pain.
Common adverse effects include high blood pressure, nausea, sweating and problems with urination.
NRIs
NRIs block the reuptake of norepinephrine (and possibly dopamine) with very little (if any) effect on serotonin. This class of medications includes reboxetine (Edronax), atomoxetine (Strattera) and bupropion (Wellbutrin).
NRIs are often quite stimulating and have been used to treat conditions like chronic fatigue, narcolepsy and ADHD. Bupropion is also used in smoking cessation. Side effects include dry mouth, insomnia, nausea, headaches and stomach upset. Weight gain is uncommon.
Tricyclic Antidepressants
Tricyclic antidepressants (TCA)s affect a variety of different receptors and neurotransmitters, which is why they can help various ailments, but also tend to be heavy on side effects, especially sedation and weight gain. The most commonly used drug in this group is amitriptyline (Elavil).
MAOIs
Monoamine oxidase inhibitors block the action of monoamine oxidase, which breaks down serotonin, norepinephrine and dopamine, increasing the brain levels of these neurotransmitters. They tend to be very effective antidepressants, but they can cause severe, even deadly interactions with drugs and even many common foods.
MAOI drugs include moclobemide (Manerix), phenelzine (Nardil), tranylcypromine (Parnate) and selegiline (Emsam), though their availability varies widely. Emsam is the only current antidepressant available in transdermal patch form.
Others
Trazodone (Desyrel) is a serotonergic antidepressant, but somewhat different from the SSRIs and more sedative. It has a fairly rapid onset of action. Nefazodone (Serzone) is a similar drug, but has been discontinued on most markets due to risk of liver failure.
Mirtazapine (Remeron) mostly acts through noradrenergic mechanisms, though it also blocks some serotonin receptors. It is sedative and can worsen restless legs (RLS), but can be helpful for IBS. Mianserin (Tolvon) is a similar, older drug now discontinued in most countries.
Agomelatine (Valdoxan) was recently approved in Europe, making it the first antidepressant medication acting through the melatonin receptors. It also blocks one type of serotonin receptors.
Tianeptine (Stablon) is a drug peculiar in that it enhances the reuptake of serotonin, essentially the opposite of the SSRIs. Besides depression it can help ADHD, asthma and erectile dysfunction and tends to be well-tolerated. Unfortunately it is not available in most countries.
Future Antidepressants
Many antidepressants in clinical trials don't work anything like the current antidepressants, but affect totally different receptors, such as the neurokinin receptors and beta receptors or types of serotonin receptors that the current drugs don't touch. They may help people who haven't benefited from current antidepressants, and some of them have a very rapid onset.
It will be a few years before any of these new drugs will be approved. Some "new" antidepressants are already waiting for approval, but they are not really new molecules, but new formulations of existing antidepressants (such as trazodone).
Which Antidepressant to Choose?
Generally your doctor will be choosing which antidepressant to try. Unfortunately this is based largely on guesswork, as it is not really possible to predict which drugs will work and which won't, or which will or won't cause problematic side effects for that particular person. Most people will usually be started on an SSRI.
SSRIs are usually the best choice if the person has anxiety or OCD, although all antidepressants can help with anxiety. Those who are very lethargic may benefit more from NRIs and SNRIs, as norepinephrine tends to be energizing. SSRIs are usually not the optimal choice for those with chronic pain, as pain tends to improve the most when both serotonin and norepinephrine are increased.
People with severe insomnia are usually put on the sedative antidepressants, mainly the tricyclic antidepressants or mirtazapine, sometimes trazodone. Tricyclic antidepressants are rarely used in the treatment of depression any more, because of their side effects and toxicity in suicide attempts. MAO inhibitors are similarly usually reserved for refractory cases.
