Two different forms of antidepressants are selective serotonin reuptake inhibitors (SSRIs) and serotonin and norepinephrine reuptake inhibitors ( SNRIs). SSRIs increase levels of serotonin in the brain, while SNRIs increase levels of both serotonin and norepinephrine.
Both SSRIs and SNRIs act on neurotransmitters, which are chemicals in the brain that help carry nerve signals between neurons.
To learn more about the differences between these two types of medication, keep reading, including how they function, the conditions that physicians can use them to treat, and the side effects associated with them.
How SNRIs and SSRIs work
Neurotransmitters, including serotonin and norepinephrine, which some people might call noradrenaline, are made by cells in the brain. Neurons, which are cells in the brain, use neurotransmitters to send signals to one another. Nerve signals are carried by neurotransmitters through a cell synapse.
Different neurotransmitters carry different types of signals. Some, called excitatory neurotransmitters, increase the probability of an electrical signal called an action potential being produced by the neuron. By contrast, inhibitory neurotransmitters weaken or slow nerve signals.
Serotonin can serve both excitatory and inhibitory roles, while norepinephrine is a purely excitatory neurotransmitter.
In the brain’s nerve terminals, SNRIs and SSRIs prevent the reuptake of such neurotransmitters. SSRIs block the reuptake of serotonin, while SNRIs stop both serotonin and norepinephrine reuptake.
Since the brain reabsorbs them, the reuptake process decreases the supply of neurotransmitters. Hence, reuptake inhibitors increase the availability of neurotransmitters by blocking this process.
SSRI vs. SNRI: How are they different
Serotonin helps control the body’s mood. An individual can become depressed when serotonin is too high or too low. Anxiety, suicidal thoughts, depression, or obsessive-compulsive behaviors may also result from low serotonin. An individual can feel less physically and psychologically active or aroused when serotonin levels increase, making it easier to sleep and to relax.
Both SSRIs and SNRIs increase the brain’s serotonin levels, possibly helping with the effects of different mental health conditions.
Norepinephrine also plays a part in sleep, concentration , memory, and control of mood in everyday life. People with low levels of norepinephrine may have difficulty focusing, or may have signs of depression or develop symptoms of attention deficit hyperactivity disorder ( ADHD).
SNRIs raise levels of norepinephrine, helping a person to focus and decrease depression.
Higher norepinephrine levels can trigger feelings of euphoria. However, panic attacks, high blood pressure, and hyperactive behavior can also be caused by them. Due to these effects, SNRIs may not be suitable for people with certain heart health issues, a history of panic, or problems with hyperactivity.
There is no definitive proof that either group of drugs is consistently superior to the other for all individuals. At different dosages, a person can need to experiment with various drugs or drug combinations.
It can take several weeks for both classes of drugs to work.
Do they have different side effects?
SNRIs and SSRIs also play a wide range of roles in the health and everyday functioning of an individual. Serotonin, for example , helps control the waking and sleeping cycles, appetite, digestion, and endocrine system of a person.
These diverse roles mean that a wide variety of side effects can be caused by SSRIs and SNRIs.
The particular side effects encountered by individuals differ among individuals, and can change over time or with higher dosages as well. Some individuals find such side effects more disturbing than others, so it is crucial to make your particular issues known to a doctor.
In certain situations, a person may experience no side effects, or when their body responds to the drug, the side effects may go away.
Some of the SSRIs’ most common side effects include:
- sexual dysfunction, including trouble becoming aroused, changes in libido, and difficulty reaching orgasm
- unusual dreams
- changes in sleep
- sinus infections and a sore throat
- hot flashes
In children and adolescents:
- muscle tremors or shaking
- nose bleeds
- heavy menstrual periods
- increased urination
Although less common, some more serious side effects can also occur. These include:
- suicidal thoughts or worsening depression, particularly among children and teenagers
- allergic reactions
- eye pain and changes in sight
- manic episodes
- changes in weight or appetite
- an irregular heart rate
- serotonin syndrome, which is a potentially life threatening condition
In individuals with too much serotonin intake, serotonin syndrome causes dizziness, rapid heart rate, increases in blood pressure, and other symptoms. Those taking several medications that affect serotonin levels may be more likely to be affected by it.
SNRIs can cause all of the same side effects as SSRIs.
They may also cause:
After they stop taking any type of medications, some people may even experience symptoms of withdrawal.
- forms of depression, such as major depressive disorder, seasonal affective disorder, and the depressive episodes of bipolar disorder
- anxiety disorders, such as generalized anxiety disorder, phobias, and obsessive-compulsive disorder (OCD)
- post-traumatic stress disorder (PTSD)
- suicidal thoughts
- fibromyalgia and other types of chronic pain
Diabetic neuropathy can be treated by certain SNRIs. Doctors can also use these medications to treat other conditions, such as sleep disorders, on an off-label basis.
Examples of SSRIs and SNRIs
While many drugs sit within one of these two categories, each specific drug behaves a little differently in the body. A person who does not like one member of a drug group’s side effects may still do well on another drug belonging to the same category.
For example, a 2014 study of SNRIs showed substantial variations between the drugs in terms of side effects, the particular conditions for which the drugs were approved by the Food and Drug Administration ( FDA) and their effects on other neurotransmitters, such as dopamine.
Some examples of SNRIs include:
- venlafaxine (Effexor XR)
- duloxetine (Cymbalta)
- desvenlafaxine (Pristiq)
- milnacipran (Savella)
- levomilnacipran (Fetzima)
Some SSRIs include:
- fluoxetine (Prozac)
- citalopram (Celexa)
- sertraline (Zoloft)
- paroxetine (Paxil)
- escitalopram (Lexapro)
- fluvoxamine (Luvox)
- vilazodone (Viibryd)
Both SNRIs and SSRIs can assist treat a wide variety of mood issues, as well as some other conditions, such as chronic pain.
If an individual takes these medications under the supervision of a physician, the quality of life may be significantly improved.
Too much of any neurotransmitter, however, can affect health and well-being negatively. Therefore, people seeking care for mental health should share all their symptoms, their full medical history, and a list of all the drugs they are taking, including supplements and over-the-counter medications, with their doctor.
To find a drug that works can take time and a little testing, so people should try to work with a doctor who is willing to discuss all options and listen carefully to questions about side effects.